03-23-2008, 07:07 AM
Join Date: Apr 2006
| | Re: Calcium Carbonate to raise KH
I would think that coral sand in the filter would dissolve better when the pH is acidic (when you need it the most) .....[/QUOTE]
Good point. That is, when you need it most, it will be there.
Remember that KH and pH both influence each other. That is, acidity can lower KH by converting the bicarbonates into CO2 which goes off as gas and/or is taken up by plants. I'd want to make sure that the tank ecosystem isn't constantly generating acid (my book, pages 4 and 5). For example, nitrification is a strong acid-generating reaction that will certainly reduce both KH and pH. This could easily happen in softwater tanks where the fish and biological filtration outbalance plant growth.
If your tank has a normal GH (over 4) and zero KH, that would tell me that acidity might be the problem. That is, the tank is generating acid that dissolves the hardwater generators (CaCO3, CaHCO3, MgCO3, etc) just fine. This reaction inevitably releases Mg, Ca, and bicarbonates in similar proportions. The released Ca and Mg will stay in the water and increase the GH. BUT, the bicarbonates can be converted by acid to CO2 and lost from the tank (CO2 degassing and/or plant uptake of CO2).
I hope this makes sense.
Rohape, I couldn't get to your website, so unfortunatley, I don't have your tank specs. However, I'd like to know if your plants and fish are doing okay? It could be that plants are drawing down the pool of released bicarbonates and CO2 faster than you can measure the KH. If your plants are growing well, your fish are fine, and you are not artificially injecting CO2, a low KH in an NPT may not be a bad thing.
That said, I would make sure you've got a little bag of something in your filter (my book p. 87). Water hardeners and alkalinity sources can be coral sand, oyster grit, egg shells, crushed seashells, Tum tablets, etc. Try to crush these sources up a bit as the more pulverized they are, the faster they will dissolve.