The Importance of Total Dissolved Solids in the Freshwater Aquarium


Retired Staff
Apr 8, 2009
The Importance of Total Dissolved Solids in the Freshwater Aquarium

Written by Niels Jensen
(posted on Plecoplanet with permission of author)


I would like to stress that this page is based on my own experiences, observations, emails, and various information sources. This is to say, that there may be discrepencies and interpretations that may be perceived differently by different people. I am open to all discussion, opinions, and remarks. Please email me (see index page-press the home button at top of page) if you, the reader, wish to comment or ask about the information contained within this article. Hope you learn something...


(Ram picture courtesy of Vincent Lafon)

One the most fundamental but unfortunately overlooked aspects of low pH fish is the consideration of TDS or Total Dissolved Solids. When I first made the decision to manipulate my water chemistry in order to make it suit the natural water parameters of dwarf cichlids, such as the popular German Blue Ram (Mik(c)rogeophagus ramirezi), my main concern was lowering pH. After all, this is what we as hobbiests always seem to be hearing and talking about. So I lowered my pH to standards I knew for sure matched their general pH levels; I even cross-checked KH and GH. I did this with many different species of dwarfs - from ramirezi's to apistogramma, and cacatuoides, yet it didn't seem to make a difference. In fact, I ended up killing some of the fish and was rather bewildered about it since I knew I had matched the fishes local water conditions to the best of my ability (and taken long acclimation times into account). Granted there are many factors that interplay in the successful breeding of these fish, and it is indeed dependant on individual water sources and general experiences, there is one extremely important factor that must be taken into consideration by everyone : Total Dissolved Solid or TDS (also referred to as Total Dissolved Salts).
The one thing I have learned (and with the help of other more experienced aquarists) is that TDS is something one must consider when manipulating water. This holds true for pretty much all low-pH fish. Remember this : low pH fish are actually low TDS fish. I will attempt to explain this in the following article.
-It must be noted that the hobbiest's own water parameters are what will ultimately determine how and if the water should be manipulated but this should become self-explanatory throughout the article.
-Also, in general, and especially for those aquarists that are relatively new to the hobby, it is best not to manipulate your local tap water but buy fish that can readily live in this water. Stable pH,GH, KH, and TDS conditions are more important and easier to handle than attempting to callibrate your water to a fish's local water conditions, unless of course, you have completely unsuitable conditions. Stability is the key word.

So what exactly is TDS and why is it important?
Here is a definition of TDS as I see it : it basically refers to all the inorganic dissolved solids in water. It does not necessarily provide foolproof information on hardness measurements (though it does include things like calcium and magnesium) but gives a better over-view of the total mineral content of water. So it is not correct to simply regard TDS as an indicator of hardness, i.e. how much calcium carbonate is dissolved in the water. One can say that there is no accurate relationship between hardness and TDS. GH is basically a measurement of divalent cations, namely MG++ (magnesium) and CA++ (calcium) where as KH is a measurement of carbonate concentration.* Both GH and KH can affect hardness and TDS levels, however, the reverse is not necessarily true. Aquarium water can have a high TDS level but a low GH and KH.
TDS thus incorporates dissolved ionic minerals, both cations and anions, Cations are elements from the left side of the periodic table (metals) and when they react they usually become positive ions. Cations include ions such as sodium, pottasium, magnesium, calcium, barium, zinc, iron and copper. Elemetns from the right side of the periodic table that react with metals take electrons to form negative ions called anions. Anions include ions such as fluoride, chloride, bromide, iodine, sulfide, chlorate, nitrate, premanganate,, sulfate, and phosphate (Source : Chemistry department, University of Florida). All these ions an other inorganic ions are included in TDS. It does not include things like H2O, or suspended particles such as wood pulp though Lenntech states that it does.
This is where things get interesting in my opinion.
In addition to above, AquaChek states the following : "In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water. Parts per Million (ppm) is the weight-to-weight ratio of any ion to water. Conductivity is usually about 100 times the total cations or anions expressed as equivalents. Total dissolved solids (TDS) in ppm usually ranges from 0.5 to 1.0 times the electrical conductivity."
As I stated earlier, TDS values are important for breeding many soft water dwarf cichlids (and many other fish species) but I will provide my own experiences in the segment further down the page.

"Similar to TSS (Total Suspended Solids), high concentrations of TDS may also reduce water clarity, contribute to a decrease in photosynthesis, combined with toxic compounds and heavy metals, and lead to an increase in water temperature" ( source : KanCRN website).

Total Solids
Here are some other things to keep in mind :
Total solids basically refers to matter both suspended and dissolved in water and is also related to conductance and turbidity (cloudiness of water).
Total suspended solids refer to the amount of total solids that can be withheld by a filter such as decaying plant and animal matter. Dissolved solids are thus the amount of matter that can pass through the filter.
It can be said that increased levels of TSS also have consequences though this is relatively obvious : high levels can block out light and thus reduce photosynthetic activity and, depending on the amount of surface agitation (oxygenation), gradually decrease the amount of oxygen produced by the plants. Decaying plant matter will use up even more oxygen and reduce the amount of dissolved oxygen in the aquarium. TSS also absorb heat and increase surface water temperature (Mitchell and Stapp, 1992; KanCRN website).
"The decrease in water clarity caused by TSS can affect the ability of fish to see and catch food. Suspended sediment can also clog fish gills, reduce growth rates, decrease resistance to disease, and prevent egg and larval development. When suspended solids settle to the bottom of a water body, they can smother the eggs of fish and aquatic insects, as well as suffocate newly hatched insect larvae." (Source : Boulder-Basin).
The previous sentence seems to relate more to natural surroundings rather than a well maintained tank, though the effects will become apparent if the conditions are bad enough. I do believe that elevated concentrations of TSS and TDS will affect the growth rate of fry.

How is TDS measured?
The total amount of dissolved substances are expressed in ppm of NaCl (sodium chloride) – TDS can be compared to conductivity and most experts recommend an approximate conversion formula of TDS (ppm) * 0.64 EC /microSiemens per cm (conductivity = basically a measurement of electrolytes).*
The easiest way for aquarists to measure TDS levels is via conductivity tests (performed using a TDS or conductivity meter in microsiemens/cm, which measures the sum of ions in the water and the conductivity of the water respectively; laboratory experiments often involve measuring the dry weight of solids remaining after evaporation. For the most part, TDS meters are calibrated with a solution of Sodium chloride and conductivity meters are calibrated with a Potassium solution (Souirce : Adrian R. Tappin December, 2000).
Technically, TDS meters will measure both insoluble and soluble substances, but conductiviy meters will not measure insoluble substances like calcium carbonate (it is my understanding that calcium carbonate does not break up into ions (not conductive), but the molecules separate from each other and are dispersed in the water). Hanna Instruments have combination meters that use a conversion factor to change EC (conductivity in microsiemens) to TDS (ppm or ppt). According to Hanna it does not matter which one you use, since they use the standard conversion for tap water of 0.5. In other words, an EC measurement of 1000 microsiemens is converted to a TDS measurment of 500 ppm. Many combination meters (TDS/EC/pH/temp) allow conversions to be adjusted between 0,45 and 1,00. This means one can set the meter to 1,00 in order to reconsititute r/o water that does not have carbonate buffering and this should give a more accurate TDS measurement.

The one drawback there is with TDS measurements is that it does not say which ions are responsible for the conductivity (though it does indicate how much of the calibration salt will make the water conductive - about 0,5 ppm of NaCl will increase conductivity by 1 microsiemen/cm). For more information on TDS meters, take a look at Automated Aquarium Systems Conductivity FAQs.

Electronic TDS meters basically measure the conductivity of water ( = how well the water conducts electricity i.e. measurement of electrolytes). The larger the concentration of ions, the higher the conductivity of water, and the higher the TDS level is = our dwarf cichlids do not appreciate this! In other words, pure water such as deionised water is not a good conductor (very low TDS levels but a tank full of it is too low for dwarfs since they lack sufficient electrolytes) but as soon as you add dissolved solids, many of them disassociate into ions and the conductivity of the water increases and thus so does the TDS level. This basically explains why conductivity is a relatively sound means of measuring TDS.
*It should be noted that there is no precise means of converting TDS measurements to the hardness of water. In fact, there is no meter that measures carbonate hardness and those companies stating that they do are basing their meters on EC measurments - reagent tests are still the most commonly used test though spectophotometers can measure color changes more precisely.
*Automated Aquarium Systems states that there will be a 2% change (increase) /degree C. Organics have very different temperature curves. Some meters will automatically compensate for changes in temperature.

A few general observations on TDS
Water becomes electrically charged once it reaches a TDS count of 50 ppm, meaning it can conduct electricity at this point. In addition, regulations on drinking water standards dictate that a limit of 500 mg/l of TDS must be held for drinking water. Higher levels can be a contributing factor for corrosion in plumbing and affects clothes washing. The aesthetic quality of water is also disrupted at levels higher that this.
AquaChek has some other general observations about TDS : "Water with a high TDS count is also typically a base (slightly alkaline) substance, meaning it is lacking hydrogen molecules, and will search for hydrogen molecules in the body to balance itself. Slightly alkaline (base) water, in short, often causes de-hydration on the cellular level! Water with zero TDS on the other hand, cannot become electrically charged, and therefore has an acid pH measurement, which simply means it is pure water loaded with positively charged hydrogen (H+) molecules, providing superior hydration at the cellular level."

TDS and Low ph fish
As I stated earlier, when we talk of softwater fish or low pH fish, what we really are saying is that they are low TDS fish. Even though many of these low TDS fish have adapted to harder, higher pH water, (and often relatively higher TDS levels), there is one fundamental problem, especially for South American dwarfs : the eggs cannot adapt well in calclium and magnesium rich water, and cannot hatch. My own experiences tell me that high TDS levels (in my case, mainly due to high levels of calcium and magnesium ions) are the culprits. This is where I used to make mistakes. I would use different methods for lowering pH and hardness but would take no consideration of TDS values. Peat can solve this problem.
I now use peat to successfully lower calcium and magnesium levels and thus pH (as well as KH and GH), as well as TDS. Many of the dwarfs I tried this with seemed to be much more content and this was reiterated by their ensuing fry (cacautoides, apistos, ramirezis, and other S.A. dwarfs.
If you match your own water with the fish's natural water chemistry, keep TDS levels low. My own experiences have taught me that the mineral content of the water, specifically magnesium and calcium, followed by carbonates and bicarbonates are the main reasons for the unsuccessful breeding of many South American dwarfs (they don't care for salts). Putting too much emphasis on pH does not solve the problem since one can say that pH is a kind of symptom of the mineral content of the water, not the actual cause. When you think of breeding dwarfs, think TDS.
In addition, it is my understanding, though I have no technical data or proof on this, that the blackwater rivers in South America are low in TDS levels, and basically sport some of the cleanest natural rivers in the world. According to Mongabay, "blackwater rivers are very low in dissolved minerals and often have no measurable water hardness. The very acidic, almost sterile water, with a pH between 3.5-6, keeps parasite and bacterial populations to a minimum… often compared to "slightly contaminated distilled water… blackwater rivers are nutrient poor."
Whitewater rivers are richer in minerals compared to blackwater rivers, and often sport a slightly higher pH and are generally much more laden with minerals and nutrients. It is important to note that the rivers are not uniform and there can be drastic changes in water chemistry especially when comparing black-, white-, and blue-waters. "Because whitewater rivers are often fed by a large number of acidic tributaries, they are relatively soft in terms of water hardness due to their relatively low mineral content and have a slightly acidic to neutral pH (6.3-7.0)" (souce : mongabay).

What I concluded for my own tanks
This part will be updated with TDS/conductivity readings in order to provide more technical data and shed light on peat's ability to lower TDS.

Many aquarists often find themselves faced with local water conditions that do not match the fish's local water conditions. In my case, both pH (7,9), GH (33 dH; Calcium 188 mg/l; magnesium 33 mg/l) and KH-alkalinity (23dH; bicarbonates 392 mg/l) are extremely high for breeding dwarf cichlids so I need to lower them.
I had to forget about just concentrating on permanent (and temporary) hardness a la KH and GH and especially just pH. I do concentrate on lowering calcium and magnesium hardness since this affects the egg membranes (they harden and make sperm penetration extremely difficult if not impossible - this is also supported by Rob Harlan, Back to Nature). Manipulating the water with just plain peat solved the problem of hardnessl, pH and TDS.

I often mix peat treated water with RO water (sometimes bottled water) as well as tap water to acquire the necessary water parameters that suit the dwarfs in my tanks. (I often include tap water in order to secure safe KH levels in order to keep the pH stable). TDS readings between 70 and 110 ppm have proven necessary for my tanks and I place a lot of emphasis on stable KH conditions that usually lie between 3 and 8. Not only do newly purchased dwarfs survive in my manipulated water, they thrive and breed, and yes, the eggs do hatch and the fry survive.

TDS considerations : Water Changes
I now also regard TDS levels as a means of deciding on when to do a water change. A rise in TDS levels means I need to change some water and thereby lower TDS levels. Rapidly increasing TDS levels can also indicate over-feeding, an over-stocked tank, or general bad maintenance. This is a practice often used by Japanese Koi breeders, in fact, it is one of their most important parameters for maintaining healthy Koi and optimal growth.

The Myth of pH Shock? Osmosis :Transferring fish from one tank to another
Here is another useful function of TDS I have found to be interesting to bear in mind. TDS levels can represent different states of osmosis. It is broadly believed fish that succumb to 'pH shock' do so due to the sudden change in TDS levels which greatly affects osmotic pressure - the fish's regulatory mechanisms cannot adapt fast enough to the change and hence the fish goes into shock and can in many cases die. It is not necessarily only due to 'pH shock' as it is often referred to.

According to Mitchel l and Stap, 1992, changes in TDS concentrations (especially when moving a fish from one tank to another) are often stressful/harmful for a fish since the density of water plays a significant role in the flow of water into and out of an organism's cells. When people talk of pH shock, I often think TDS shock due to changes in osmotic pressure.

One can say the TDS readings help give an understanding of the difference in osmotic states between one tank and another. Differences in TDS levels appear to represent differences in osmotic states fairly well, thus the more total dissolved solids i the water compared to the amount of solids in the tissue of the fish will cause the fish to lose fluid via its gills. In my humble opinion, TDS meters are often disregarded as a tool that can be used to give a good indication of how successfully a fish will adapt to the water in one tank to another.
It is my experience that a fish taken from similar low levels of TDS will not die even if the difference in pH is considerable, though this definitely does depend on the species, age, and general water conditions and requirements of the fish. In my humble opinion, TDS meters are often disregarded as a tool that can be used to give a good indication of how successfully a fish will adapt to the water in one tank to another.
Wright Huntley from Fremont CA, USA has also taken notice of my own and many other aquarists' observations : "IMHO tds (total dissolved solids) is far, far more important than hardness to the fish. It has a direct effect on the osmotic regulatory process for their maintenance of body fluids. 99% of reported "pH-shock" cases were probably from sudden drop in tds. That causes cells in gills to explode as they take in too much water. Going the other way (to higher tds) is dehydrating, but seems to be less fatal, usually. Drip acclimation to major changes in tds is always a good idea. That allows the complex three-level osmoregulatory process to adjust slowly to the new water." Souce : Wright -- Wright Huntley, Fremont CA,

Various Aquarium Products:
Activated Carbon
Stated short and simple, carbon will reduce organics and oxidants in the water, including most particulates, however, it will not significantly reduce TDS and hardness in my experience.
For us aquarists, carbon formed from bituminous coal is often used to remove dissolved organic compounds (DOC's) from the aquarium (wide range of pore sizes). As far as I understand, carbon will always contain phosphates, so if a manufacturer says it does not, it is either unaware of it or lying – since all carbons are organic in source, they will contain phosphates (acid washed carbon will contain less phosphate). I have recently read that carbon can increase pH level in a tank though this does of course depend on local water chemistry and amount of carbon used (source : drhelm).
Companies will sometimes use Activated carbon pre-filters for RO and DI systems containing GAC (Granulated Activated Carbon) in order to remove chlorine, chloramines, organic coumpounds, and pesticides though they will not remove a sufficient quantity of ions that would otherwise result in softer water (source : SpectraPure Carbon Filters). Granular activated carbon removes via adsorption.
It seems to be generally agreed upon that carbon will remove chelated metals There has been much research on activated carbon's ability to pull various elements from the water. According to drhelm the absorption potential of various substances by activated carbon includes the following :

High to Very Good:Arsenic, bleach, chloramine, chlorine, chromium, colors, dyes, gold, insecticide, odors, monochloramine, tin

Good to moderate: Acetic acid, cobalt, detergent, hydrogen sulfide, mercury, ozone, potassium, silver, soap, solvents, vinegar

Fair: Copper, iron (not chelated)*LINK Bottom of Page, lead nickel, titanium, vanadium

Low to None:
Alkalinity, ammonia, barium, carbon dioxide, hardness, copper, manganese, nitrates, selenium, molybdenum, zinc

An email from Justin P. Healy states his own experiences with activated carbon and iron.

Note : Shawn Keslar, a chemist at WVU NRCCE Analytical Laboratory has performed an analysis of activated carbon's ability to 'eliminate' trace elements.
It should be noted that there is still a bit of controversy, conflicting opinions and experiences, and not enough data about the efficiency of activated carbon and this very general guideline is by no means completely correct.

Blackwater extracts
These products often add some forms of tannins and other organic agents to the water, however, I do not place much confidence in general with these products and until a company can technically prove that the product lowers TDS levels, I do not believe it. I do not think a company is interested in even bringing the matter up since most aquarists are not aware of this factor, only how close they can get their tank to assimilate blackwater conditions. In general, these products cannot reproduce true black water as it is found in nature. It should also be noted that they are often phosphate based, and can be a contributing factor to algae blooms.

Deionized Water
Deionized water will lower TDS levels, though since the water is tripped of all minerals, fish would not be able to survive in it and one would need to add these minerals and salts with normal tap water. Deionized water works by pulling water through a cylinder that contains a chemical resin which strips the water of mineral ions that otherwise would coalesce to create hard water. These chemical beds do not add anything to the water, but remove minerals (as opposed to household water softeners that add sodium or potassium ions – instead of leaving Calcium carbonate spots on glass, water softeners may, to a degree, leave i.e sodium carbonate spots).

I have written an article on peat here and this article on TDS is basically a result of my endeavours with the stuff. It has been a concoction of trial and error though it all ended with promising results. Peat will lower pH, GH, KH, and TDS (lots of testing). At the end of the day, it all depends on your own water conditions and how much the peat treated water affects TDS. As previously stated, I often mix the peat treated water with RO (and some tap) water until I attain a stable chemistry that suits the fish and its eggs.

Why not just forget about peat and use a combination of tap water and RO water?
Well, you basically can, and depending on the species of fish, you may very well just as successfully breed dwarf cichlids without the combination of peat treated water. Call me old-school, but I honestly believe that peat water (even small additions) are positively regarded by many, if not most, of the low TDS fish, especially dwarfs such as Rams and Apistos. The addition of tannins, phenols, humic acids etc...allow me to get a little closer to natural conditions (i.e. black water) and have proven to increase my own success rate in breeding the little buggers.

RO (Reverse Osmosis) Water
The number of RO systems are overwhelming. Researchers have discovered how the principles of osmotic pressure can help 'purify' water. Using a membrane and feeding water with sufficient pressure to overcome the osmotic pressure of the two waters on each side of the membrane, we can 'manufacture' clean water on the side of the membrane that has no pressure. Water originating from RO systems have generally been removed from between 80 and 98% of all sediment, pollutants, various ions, bacteria and other pathogens and contaminents. SpectraPure (pressure operated) Reverse Osmosis Units are documented to remove over 98% of all ionic impurties and 95% of all organic impurties, as well as other colloidal and particulate impurities. This holds true for most RO systems and as a consequence, TDS levels are drastically reduced.

Here's another huge myth that has thrived in the aquarium trade for years and years. Let me start by simply saying : adding salt to an aquarium will not lower TDS levels and it is generally not something that will contribute to the well-being of low TDS fish though there are certain situations where salt will be of benefit. I have yet to find well-documented data that proves how the addition of salt will act as a disease-preventative (prophylactic). It is generally not a stress-reliever for fish that naturally enjoy low TDS levels.

I have taken the liberty of putting in a link to an excellent article by Robert T. Ricketts, named The Salt of the Earth...The Salt of the Sea. This should provide a good understanding of the many myths associated with salt in the aquarium (I know a few local fish stores who should read this article!). WetmanNY also has an excellent page (and site) well worth a read.

Water Softeners
Water softeners do indeed soften water, however, they do not reduce TDS levels. Salt-exchange resins work by replacing calcium and magnesium ions with sodium or potassium ions. A standard GH and KH test kit will show that the water is softer but a TDS meter may show an even larger increase in TDS levels. As far as I understand, water softeners use i.e. two sodium ions to 'eliminate' one calcium or magnesium ion. states that "for every grain of hardness in your water, 7.5 mg of Sodium will be *added* to each quart of water by the ion-exchange method. If you have water that is 10 grains per gallon hard; you will add 75.0 mg of Sodium per quart of water softened by ion-exchange."
A post-exchange resin water will end up being even more different than tap water and especially when compared to a fish's local/native water. The only thing it is good for is washing your clothes and making coffee (fewer bubbles and scum) and this is not something you want to do in the aquarium!
Here is an interesting account of a fish importer of South American cichlids who experienced a high mortality rate due to a water softening system that exchanged calcium and magnesium ions with sodium ions. The result ended up in the use of a natural media called clinoptilolite, a type of zeolite, and the endevour is described in an article written by Timothy A. Hovanec, Ph.D, called Ion Exchange - What It Is and When To Use It (from Marinelandlabs).

Bottled Water FAQ
The following link provides information on what the different types of bottled water are : Artesian Water, Fluoridated Water, Mineral Water, Municipal Source Water, Soda / Seltzer / Tonic Water, Sparkling Water, Spring Water, Structured Micro-Cluster Waters, There is no information on TDS levels, just general definitions and desctiptions. In general, bottled water has reduced TDS levels, though this will vary from company to company and country to country. There is usually an indication of conductivity on the bottle labels as well as measurements of what minerals and other elements are found in the water.

Further Information (in no specific order)
Important Water Quality Factors for Fish and Plants is a very informative article on common water quality parameters important in drinking water, wastewater, and natural water. Many parameter listings include descriptions of the effects of analyte levels on living organisms and give an insight into how they can be applied to aquariums.
WATER QUALITY CONSIDERATIONS FOR AQUACULTURE (PDF file) by Robert C. Summerfelt Department of Animal Ecology Iowa State University Ames, IA 50011-3221
Basic water chemistry and other important water parameters.
The properities of, and its importance to life : water.
A look into what constitutes natural water; ions present in it (hydrology) and much more from the University of Waterloo.
General info on water and different filtering mechanisms that reduce TDS and harness : The Water Treatment FAQ.
Below are a number of articles written by Dr. Timothy A. Hovanec, Chief Science Officer of the Aquaria Group. Many were published previously in Aquarium Fish Magazine or Aquarium Frontiers Online.

Dictionaries and Glossaries

AQUATEXT.COM is a dictionary that is sponsored by Pisces Engineering Ltd and is written by aquaculturists for aquaculturists.
Glossary of Environment and Microbiology Terms from Bioaquatic Supply Corp.
Here is a great Water Glossary by the Dutch company Lenntech.

Lake and Water Word Glossary from Bioaquatic Supply Corp.
Lake and Water Word Glossary by the North American Lake Management Society
General Aquarium Glossary from
Cyberspace Chemistry (CaCt) from University of Waterloo

A few conversion explanations :

"Water hardness is expressed in a confusing array of scales, although in the aquarium hobby the influence is to express them in terms of milligrams per litre of Calcium carbonate (mg/L CaCO3), which is also equivalent to parts per million, and degrees German Hardness (dH). For aquarium purposes, you can use the following conversion factors:"
dH × 17.9 = ppm
ppm × 0.056 = dH

(Taken from WATER HARDNESS - Copyright 2000, Adrian R. Tappin Updated December, 2000)
"Parts per million or grains per gallon are the most common. One part per million (PPM) is just what it says: out of one million units, one unit. Grains, or grains per gallon (GPG) is a weight measurement taken from the Egyptians; one dry grain of wheat, or about 1/7000 of a pound. It takes 17.1 PPM to equal 1 GPG. In other words, if your water has 171 PPM calcium in it, divide 171 by 17.1 to get the answer in grains. This example would be 10 grains, or GPG." (Taken from :

°dH Description
0 - 3 soft
3 - 6 moderately soft
6 - 12 slightly hard
12 - 18 moderately hard
18 - 25 hard over 25 very hard

by "Justin P. Healy"
Date: Fri, 7 Mar 1997
"I was told again and again that carbon would not absorb iron. My father-in-law, a water-purification engineer told me carbon could not absorb iron. This conflicted with the reality I had experienced so I did a simple experiment.

Into a ten gallon tank of freshly carbon-filtered water I poured chelated iron until I got a reading in excess of 3 ppm. We're talking purple. I filtered the water through a freshly cleaned and loaded 350 gph carbon filter. In no time at all the iron fell to unmeasurable levels. Since then I have used gravel and peat in my filters.
The suggestion that it is the chelating element that makes carbon able to adsorb iron would make both my father-in-law right and me right.
Thanks for the information."

Axelrod, Herbert R. "The Golden and Normal Ram: Microgeophogus (Apistogramma) ramirezi." In Breeding Aquarium Fishes, Book 2, T.F.H. Publications, Neptune City, NJ, 344-352.

Boyd, C. E. 1990a. Water quality in ponds for aquaculture. Alabama Agricultural Experiment Station, Auburn University, Auburn, Alabama.
Kullander, Sven O. 1977. "Papiliochromis gen. n., a New Genus of South American Cichlid Fish (Teleostei, Perciformes)." Zoologica Scripta, 6: 253-254.
Langhanuner, James K. 1991. "The Ram and its Nomenclature: Which Name Actually Has Precedence?" Buntbarsche Bulletin, 147:18-19. Leibel, Wayne S. 1983a. "On the Identity of Geophagus acuticeps Heckel 1840: Part II." Buntbarsche Bulletin, 95: 11-19.
Leibel, Wayne S. 1993d. "Cichlids of the Americas - Part 15: Eartheater Update." Aquarium Fish Magazine, 5 (12): 52-59.
Michaud, J.P. 1991. A citizen's guide to understanding and monitoring lakes and streams. Publ. #94-149. Washington State Dept. of Ecology, Publications Office, Olympia, WA, USA (360) 407-7472.
Piper, R. G., I. B. McElwain, L. E. Orme, J. P. McCraren, L. G. Flower, and J. R. Leonard. 1982. Fish hatchery management. U. S. Fish and Wildlife Service, Washington, D. C.
The GREEN (Global Rivers Environmental Education Network) Hands-On Center.
USDA (U.S. Department of Agriculture). 1996. Aquaculture outlook. U.S. Department of Agriculture, Economic Research Service, Washington, D.C. Report LDP-AQS-4, October 8, 1996.
U.S. EPA Office of Water, Current Drinking Water Standards.

Many Thanks to Niels Jensen for allowing us to put this article in the Plecoplanet articles forum and on the website

Apologies if any of the links within the article are broken.

Link to archive of original article


Retired Staff
May 6, 2009
Berkeley, CA
just a quick thing--

the only way the addition of a solution (i.e. blackwater extract) would lower tds levels would be if it precipitated the aforementioned solids. i don't know if the stuff has these capabilities, and even if it did, it can't possibly be good for the tank "ecosystem".


Global Moderators
Staff member
May 5, 2009
Wiltshire nr. Bath, UK
Hi all,
This is another good quality article, and a good find. The peat article is worth a read to:

I like to have some DOC (dissolved organic compounds) in my tank water for soft water fish. The TDS lowering capabilities of humic and fulvic acid producing additives (peat etc) are due to the negatively charged carboxylic acid groups which complex metal ions and precipitate them out of the tank water. I've never used commercial "black water" treatments and can't imagine they offer any advantages over treatment with any of sphagnum peat, alder cones, tea leaves, oak leaves, Indian Almond leaves or cork bark.

I'm using Alder cones and Camellia, Loquat & Oak leaves (they all work) at the moment, rather than purchased horticultural peat or Indian Almond leaves, but only because they are sustainable and free.

cheers Darrel