This is my first post in this forum so I may be posting this in the wrong place. I've asked this question in 2 other forums and still no answer. I have 2 tanks a 29 gallon low tech and a 10 gallon hospital tank that I have neon tetras recovering from columnaris in. Here's my problem. My tap water comes right out the tap at a ph of 7.4 and a kh of 5-6dkh. After 24 hours with an air pump ph is 8.2 and kh is 10. This is all good and well but in the 29 gallon ph is 7.4 with a kh of 3dkh and the 10 gallon has a ph of 7.8 with a kh of 5dkh. After just days the kh decreases significantly and that leads to the lh to drop. I have nothing that could lower ph like peat moss or driftwood (because my 10 gallon is empty since its a hospital tank and my 29 gallon is pretty empty except for a crypt and some guppies) and the nitrate in the 10 gallon is only 10ppm and nitrate in 29 gallon is 20ppm. I live in Franklin Kentucky and all the water reports say hard water which I know. I don't want to have to use crushed coral because a 10 kh should be enough. So my question is why is my kh and ph decreasing at such a rapid rate?