I just started a 20 gallon tank for my betta, but the ph is WAY too high. In my 10 gallon tank (where my betta currently lives) it is at 7.5 which isn't that bed. In the 20 gallon tank though it is over 8.5 which is way to high for any fish. The only difference I can think of is that the 20 gallon has sand and the 10 gallon has gravel. I bought normal black sand at petco, so I don't know why it would affect the ph. I paid $40 for it so I really don't want to get rid of it.
I want to keep cory catfish with my betta and they need sand, so I can't get gravel. I don't want to get into adjusting the ph because that is very difficult and I'm very inexperienced with fish. I really want to keep bettas and cories so what can I do to make my cage work? I can replace the sand if necessary, but I don't know what else I could get. I want the sand to be black so play sand wouldn't work. What should I do?