PH drop?

[Tener ds]

hi all,wot would cause a ph drop?
just done a water change on my edge and a test and the ph has gone down from 7.5 to just under 7.
the only change was removing my carbon from the filter cos it was very blocked up and well passed its replacement date, and the store where i get them from have run out off them.

 

[Irene0100]

what ph was the new water you added?

 

[Tener ds]

what ph was the new water you added?

just checked it. it was just a nats higher,more 7 than under but still lower then last week.
would this little drop harm th fish?:dk:
also would this be down to the water board :dk:

 

[VickiandKev]

Ok this is weird!.. Just done a water change on my starlight tank and the pH was 6.5-7.0 and hardness 235 TDS. We only use tap water on that tank, haven't added anything and last did a water change a week ago?!? Explain that one lol :S

 

[dw1305]

Hi all,
When the pH is around pH7, you can get relatively large changes in pH readings as the CO2 content of the water varies etc. You have to remember that pH is a strange measure, it is a both logarithmic scale (log10), and it represents the actual acidity or alkalinity of a solution as a proxy of the inverse number of H+ ions.

The reason for these changes around pH7, is that at pH7 (neutral) there are equivalent numbers of OH- and H+ ions (H2O disassociates to H+ and OH- ions), so any small additions of ions to either side of the equation will cause a relatively large change in pH.

pH6 is 10 times "more acid" than pH7, but pH5 is x100 and pH4 x 1000 more acid than pH7 (and the same relationship with alkalinity for pH8, pH9 and pH10).

Unless water has a lot of buffering (as example the very carbonate rich, hard water of Lake Malawi or London tap) the pH can go up and down fairly widely, at pH7 you may have a lot of acid and alkali compounds neutralising one another (buffered water), or you may have very few ions of either description.

A change from pH7 to pH7.2 may be due to the loss of a small amount of CO2, even in heavily buffered water, and you don't need to worry about it. If your pH varies widely over 24hours you have very little buffering in the water, and if it rapidly changes from pH8 to pH9, you've just knocked the tub of "Bi-carbonate of Soda" (NaHCO3) into it.

cheers Darrel

 

[Irene0100]

doing a w/c can stir up grot in the substrate and affect acidity.

 

[VickiandKev]

Hi all,
When the pH is around pH7, you can get relatively large changes in pH readings as the CO2 content of the water varies etc. You have to remember that pH is a strange measure, it is a both logarithmic scale (log10), and it represents the actual acidity or alkalinity of a solution as a proxy of the inverse number of H+ ions.

The reason for these changes around pH7, is that at pH7 (neutral) there are equivalent numbers of OH- and H+ ions (H2O disassociates to H+ and OH- ions), so any small additions of ions to either side of the equation will cause a relatively large change in pH.

pH6 is 10 times "more acid" than pH7, but pH5 is x100 and pH4 x 1000 more acid than pH7 (and the same relationship with alkalinity for pH8, pH9 and pH10).

Unless water has a lot of buffering (as example the very carbonate rich, hard water of Lake Malawi or London tap) the pH can go up and down fairly widely, at pH7 you may have a lot of acid and alkali compounds neutralising one another (buffered water), or you may have very few ions of either description.

A change from pH7 to pH7.2 may be due to the loss of a small amount of CO2, even in heavily buffered water, and you don't need to worry about it. If your pH varies widely over 24hours you have very little buffering in the water, and if it rapidly changes from pH8 to pH9, you've just knocked the tub of "Bi-carbonate of Soda" (NaHCO3) into it.

cheers Darrel

thanks for that darrel that makes complete sense with our London water. I wasn't worried as the pH in the Amazon varies throughout the day from 6.5-8.5-9. To be honest I should of really figured that out but its hard to think of things as variables in stead of them being static.

thanks again

 

[dw1305]

Hi all,

I wasn't worried as the pH in the Amazon varies throughout the day....

I struggled with the relationship between buffering and pH for a long time, it didn't really make any sense until a colleague explained it to me. It seems strange but very soft, "acid" water is much more prone to large swings in pH, because it doesn't have any carbonate (dKH) buffering. This means any addition of acid will cause the pH to drop to very low levels. The same applies to any small addition of an alkaline compound (say NaHCO3), in this case there are relatively few acid compounds (humic acids from peat etc, carbonic acids from CO2) to counteract the carbonate ions and the pH rises.

This is from Diana Walstads' book. <http://www.plecoplanet.com/forum/showthread.php?t=6701&highlight=walstad>

"Daily variations of the water parameters are rarely – if ever – taken into account. Data collected in a freshwater lake (Star Lake, VT) with a very low alkalinity showed a diurnal pH fluctuation beyond the imagination of most hobbyists. Thus, the pH at 10 am was measured at 5.7 (strongly acidic), 9.6 at noon (strongly alkaline), 8.3 at 2 pm (moderately alkaline) and finally, 6.4 at 4 pm (slightly / moderately acidic). Readings were taken at a 0.5M depth. The fluctuation observed was due to the low KH value of the water (something reported for the Amazon river, too) and the presence of large amounts of phytoplankton. Under the circumstance it is extremely difficult, if not impossible, to figure what is the “right†pH for any form of aquatic life collected in that lake and which tank could cope with this kind of fluctuation. The low – high points of the day differ by 4 pH points, which means that the concentration of H+ in the morning is 10.000 times higher than at noon, while this change takes place in just two hours. It goes without saying that this pH swing cannot be observed in an aquarium only because we cannot reproduce the amount of light which falls in the Lake. In any case, if somebody reported that a suitable pH for aquatic life collected in this lake should range daily from 5.7 – 9.6 most hobbyists would think it was a typo."

There are some more pH and buffering posts here:
<http://www.plecoplanet.com/forum/showthread.php?t=4506>
<http://www.plecoplanet.com/forum/showthread.php?p=41650>

cheers Darrel

 

[Lornek8]

This is from Diana Walstads' book. <http://www.plecoplanet.com/forum/showthread.php?t=6701&highlight=walstad>

"Daily variations of the water parameters are rarely – if ever – taken into account. Data collected in a freshwater lake (Star Lake, VT) with a very low alkalinity showed a diurnal pH fluctuation beyond the imagination of most hobbyists. Thus, the pH at 10 am was measured at 5.7 (strongly acidic), 9.6 at noon (strongly alkaline), 8.3 at 2 pm (moderately alkaline) and finally, 6.4 at 4 pm (slightly / moderately acidic). Readings were taken at a 0.5M depth. The fluctuation observed was due to the low KH value of the water (something reported for the Amazon river, too) and the presence of large amounts of phytoplankton. Under the circumstance it is extremely difficult, if not impossible, to figure what is the “right†pH for any form of aquatic life collected in that lake and which tank could cope with this kind of fluctuation. The low – high points of the day differ by 4 pH points, which means that the concentration of H+ in the morning is 10.000 times higher than at noon, while this change takes place in just two hours. It goes without saying that this pH swing cannot be observed in an aquarium only because we cannot reproduce the amount of light which falls in the Lake. In any case, if somebody reported that a suitable pH for aquatic life collected in this lake should range daily from 5.7 – 9.6 most hobbyists would think it was a typo."

There are some more pH and buffering posts here:
<http://www.plecoplanet.com/forum/showthread.php?t=4506>
<http://www.plecoplanet.com/forum/showthread.php?p=41650>

cheers Darrel

One thing to consider in this instance is the fact the measurements were only taken in one location & doesn't take into consideration or report how other areas in the lake changed. One important thing to remember is that in the wild fish have the opportunity/ability to move over much greater areas than they can in an aquarium, thus if water conditions do not suit them they can move to find water that might. Anyone who may be somewhat familiar with fishing in lakes knows that fish change their locations throughout the day & throughout the season. There are most likely other fators that contribute to these movements but water conditions can be a factor. Thus, although waters may see daily variations in chemistry, this does not necessarily mean its good for aquairum fish on a day-to-day basis. I would be interested in seeing the source of the reports of daily fluctuations on the Amazon as i'd think moving water would expereince much less day-to-day variations and changes would be more seasonal.

 

[dw1305]

Hi all,
Yes I agree that Lorneks' comments are entirely valid. I think the point about the main "white water" Amazon river channel <http://www.plecoplanet.com/forum/showthread.php?p=55415> would also be true, the higher level of dKH in the white water, absence of aquatic plants and high flow rates (oxygenating as well as mixing the water) would all limit swings in pH. I also think the high level of humic and tannic compounds, and absence of plants, would limit the pH variation in "black water" streams and keep the pH from rising much above pH5 (there would be nothing to stop it falling however). As another example fish may also forage in areas with thick vegetation during the day, but be excluded from them at night because of low dissolved oxygen levels.

There are a lot of papers that look at the Amazon basin fish and adaptation to low oxygen (O2) levels (air gulping in Cories, Hypostomus, Arowanas, fry refuges in hypoxic areas etc.), where the relationship between O2/CO2, dissolved organic carbon and pH are mentioned, but not really discussed in detail.

However I've found this one from Brazil that looks at the relationship between plants and DO, and gives diurnal pH variations as well as alkalinity and conductivity values, hopefully all in the table below.

from Rocha, RRA.; Thomaz, SM.*; Carvalho, P. & Gomes, LC. (2007)
Modeling chlorophyll-α and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil) Brazilian Journal of Biology 69:2

This certainly suggests that fluctuating levels of pH are found in the "clear water" lakes and slower flowing streams, where there is abundant plant growth and biomass, combined with low levels of carbonate buffering.

Anecdotally there have been threads on UKAPS <http://www.ukaps.org/>, which discuss the changes in pH driven by the start of CO2 injection, which suggest that rapid changes of pH caused by altering the CO2/HCO3 equilibrium have little effect on fish, which wouldn't be true if you did the same by adding compounds (like an acid - HCl perhaps) to the water.

If I kept Marines, or lake Tanganyika/Malawi cichlids, from very stable highly buffered environments I would be very worried about pH variation, as I keep soft water fish I tend to ignore pH.

The reference Diana Walstad uses is: Allen, H.L. (1972) "Phytoplankton photosynthesis, micro-nutrient interaction and inorganic carbon availability in a soft water Vermont Lake" In Linkens GE (Ed) "Nutrients and eutrophication... " Symposium Amer. Soc. Liminol. Oceanogr. 1 pp 63-83

cheers Darrel