I am starting a new 20 gallon tank which will have 4 cory catfish and one betta. I planted the tank and put in black Petco sand for my cories. When I tested the ph of the tank, it was at 9 which is way too high. It may even be higher because my testing strips stop at 9.
The ph of my other tanks with gravel is at 7.5 so the only thing I can think of that would bring my 20 gallon's ph to 9 is the sand. It is normal aquarium sand so it shouldn't cause this problem. Other people on here have used this sand without a single problem and they love it so I don't know why it would be different for me.
What can I do to know for sure if the sand is the problem? I spent $40 on it so I don't want to just throw it out only to find that it wasn't responsible for the ph spike. Is there anything I can do to figure out if there could be something other than the sand that is affecting the ph? Should I try emptying out my entire 20 gallon, rinsing everything off, and starting over?