I just recently got a pair of apistos, and i want to lower the pH to about 6. i have a piece of driftwood in there, but it isn't leaking any tanins. i added pH lowerer, and it dropped it to about 6.8. i added some more, and the next day i checked and it was at about 7.4 nothing i do is lowering the pH. Does anybody have any suggestions on how to lower it.