I've got a simple 15 gallon freshwater setup for my son. The pH of our tap water runs around 6.9 based on the test strips I've been using. The seems low to me. Assuming the pH of the tank stays stable, is 6.9 okay? Or should I try to manage it up a bit? So far I've been adding pH increaser buffer to get it up to around 7.2, but it would be easier not to worry about it. The stock is platys, tetras, a couple upside down catfish, a frog, a couple shrimp, and a couple snails.