I have restarted my 20gal aquarium after learning a year ago the hard way that I didn't know enough about keeping fish alive in an aquarium. I now have it stocked with seven red minor tetras, one otocinclus catfish and one snail. I've been testing all of my water parameters and everything looks good except the pH. I'm using the API test kits. The pH is reading all the way up at 7.6 (the lowest reading). I've performed a few partial (5gal) water changes with deionized filtered water (we have a filtration setup at work where the aquarium is). When I get the deionized water, the pH tests at 6.0 (the lowest reading). I've been using Seachem's Acid Buffer (2.69g) and Alkaline Buffer (3.50g) on the 5gals of water which results in a pH of 6.6. From what I've read, this seems pretty ideal for the Tetras. I leave the replacement water for a day to make sure the pH stays the same and it always reads 6.6. After I perform the water change, the pH general goes down to 7.0. However, within a couple of days, the pH is right back up at 7.6. My dKH is 2 or 3 which actually seems kind of low. From what I understand, a low dKH should allow for a low pH, but it isn't working out that way. My GH is running about 90ppm. How is it that my pH keeps going up? Any ideas how I can get my pH down? Is there something that I'm missing?