Oyster Shell Grit, advice please

Zebra Pleco

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Nov 18, 2010
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Hi all, looking on ebay for oyster shell grit, a lot of it seems for birds is this stuff ok to use?

http://home-garden.shop.ebay.co.uk/i.html?_nkw=oyster+shell+&_sacat=1281&_sop=15&_odkw=oyster+shell+grit&_osacat=1281&_trksid=p3286.c0.m270.l1313

Or can someone recomend another listing on ebay to buy the grit. Lastly, how much do you use, I see listings for 900g bags, I am going to be placing this into a rack system containg 4 tanks measuring 48x15x15 each on a central system/sump setup.

Need to raise my GH/KH by 2 or 3.
 

Irene0100

UK Support Team
May 14, 2009
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well if not sure be careful, it could have other additives for birds like antiseptics or something, so unless you know the source and exact contents you may be taking a risk.
have you tried adding crushed egg shells?
 

Breamlegend

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Apr 22, 2009
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You would need to know the source of the oysters. ie How they were grown. I actually know a lot about this as one of my relatives is an oyster farmer and used to sell crushed oyster shell. Oysters that are grown on sticks- naturally spawned may be unsafe- depending on the coating on the sticks (used to help catch the spat). Tar used to be used and then a cement type product. Both would be unsuitable for aquarium use as this is attached to the oyster and ground up.
Farmed oysters, from baskets etc are okay. Oyster shell is very good for filtration and is used for drainage pits etc. You could just buy some oysters, eat them and then crush the shell. A lot of work though.
I have used oyster shells in my cichlid tanks without problems
 

Zebra Pleco

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Is it as easy as that buy some eggs or oysters, give them a good clean and place into tank.

How many eggs shells or oysters are we talking here. I have a four tanks in a central sump system 4 tanks of 48x15x15.

Will nip along to local farm and get some eggs, or down to the fish mongers and see whats come in today.
 

dw1305

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May 5, 2009
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Hi all,
The ordinary "Oyster shell" chicken grit should be fine, chickens are fairly sensitive birds. It is just shell grit, it doesn't have any chemicals etc. mixed with it.

A 900g is about £2.

You won't need very much, the actual amount you use will depend upon how quickly it dissolves. What you are aiming for is it to raise your KH to about 4dKH. It isn't a very easily fine tunable system, but I'd use the coarser grade (will dissolve more slowly) in a small net bag, either in the filter or near the outflow.

If you are collecting your water and storing before use you can have the grit in the storage tank. You can then measure the KH (and the TDS) to give you a rough measure of how much has dissolved. Subsequently you can just measure the TDS, as long as it is about the value recorded when the water was at 4dKH you have enough Oyster shell dissolved.

You could do this in the tank as well, but there are a lot of other factors that may effect the TDS in the tank.

cheers Darrel
 

dw1305

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Hi all,
I am assuming your water is quite soft?
Bob, you are right, it's the water from this this thread: <http://www.plecoplanet.com/forum/showthread.php?t=8904>. I think at some point in that thread (or it's predecessor <http://www.plecoplanet.com/forum/showthread.php?t=8744>) you recommended using "Kent RO right", and that is still the best option, as it is finely controllable. The only down-side is cost. Oyster shell grit will work, and is a lot cheaper, but doesn't give you the same degree of control.

The other option is to make up your own GH/KH booster with a mix of magnesium sulphate ("Epsom salts") potassium bicarbonate (or sodium bicarbonate ("Bi-carbonate of soda")) and calcium chloride.

Details here: <http://www.theplantedtank.co.uk/> under "information" > "water hardness" and "re-mineralising agent".

cheers Darrel
 

dw1305

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Hi all,
I have RO Right in the house somewhere, but when I use this is sends my TDS readings up
Stuart it will raise the TDS, you are adding compounds ("salts") that will dissolve into ions ("Epsom salts" will dissolve ("disassociate") into Mg2+ and SO4- ions).

The TDS is a direct measure of these ions.

The "Oyster shell" grit will also raise the TDS, in this case the calcium carbonate will slowly dissolve as H+ ions are exchanged for Ca2+ ions. The solid calcium carbonate (from the shell grit) will become calcium bi-carbonate (Ca(HCO3)2) from the carbonic acid (dissolved CO2) - carbonate equilibrium:

CaCO3 + CO2 + H2O → Ca(HCO3)2.

The reserve of HCO3- ions is the "carbonate hardness" that we measure as dKH. The Ca2+ ions are what we measure as dGH.

You want to raise the KH, and supply some GH, these are both parts of the TDS. Bob can do this by adding HMAS treated tap water because his tap water is hard ("has high levels of both GH and KH").

Your water is alkaline because of the added caustic Soda (NaOH), but it is very soft, it has low TDS and GH and no reserve of KH (no carbonate buffering). This means that the pH is unstable, and if the proportion of H+ ions rises above that of the OH- ions, the pH will crash

The "RO right" or shell grit supplies both GH and KH and stops the pH crashing. Hope that helps.

cheers Darrel
 

dw1305

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Hi all,
Stuart thanks, I know it is not straightforward to work out how all the bits go together.

I never really under-stood buffering properly until some-one explained it to me in terms I could under-stand, and then eventually the penny dropped.

cheers Darrel