10-13-2009, 12:16 PM
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Good to ask, we all learn that way.
The fact that your tank pH is lower than the tap (and doing the 24hr test is very wise) suggests your tap water has little carbonate hardness. It would be good to have it tested, either with your own API hardness (both KH and GH) kit or take a sample to the store. it's the KH that is important in this, but it is good to know the GH as well.
Limestone rock raises pH and hardness but slowly, as you've noticed. Crushed dolomite, coral or marble (as in such gravels) do it faster. I use dolomite gravel, about half a cup in a nylon bag in the filter chamber does it, raises the GH/KH about 1-2 ppm which is enough to maintain a stable pH at 6.0 which is where I want it. But before trying this, I would get your water tested for KH and GH. Adjusting water pH and hardness is tricky as it can suddenly swing due to this or that, and that is dangerous on the fish.