What kind of sand should I use?

I'm starting a 20 gallon long aquarium that will have 4 cory catfish and 1 male betta. I got regular black aquarium sand from petco, but it brought my ph up to 9! I'm not sure why this happened since it wasn't coral sand or anything special. I lost 2 of my cories already due to the ph and the other 2 are on the brink of death. Luckily my betta is in a separate tank due to his fin rot so he wasn't harmed by the ph.
Anyway I think I'm going to have to get rid of my sand if I want my aquarium be okay for fish. I spent $40 on that sand so I really don't want to have to buy another super expensive sand like tahitian moon. I will get expensive sand if necessary, but I would like to avoid it if possible.
What kind of sand should I get? I was thinking play sand, but I'm worried it might cause ph problems by leaking things like calcium. My tap water has a ph of 7.5 and a hardness of 180ppm so would play sand affect that? I also really want my sand to be black to go with the design of my tank and make my albino cories stand out. Is there any possible black/dark colored play sand I could get? If there's not, what is the cheapest sand I could get that wouldn't affect my ph? I don't want to have any more problems with the sand so I want to get the best thing for my tank.