Yeah, Most aquarium sand and gravels are inert, won't affect pH, but African Cichlid substrates intentionally increase the pH. Just look for things that say they "Will not buffer" on the bag. Is yours one of these: http://www.caribsea.com/pages/products/cichlid.html ? If you read they say things like "It buffers automatically for the life of the aquarium". Check the bag yours came in (if you still have it) and see if it says something like that.
I'm planning a planted tank with Eco-Complete for Angelfish. Eco-Complete says "Will not increase pH or Carbonate hardness in the long term" (http://www.caribsea.com/pages/products/planted_aquar.html). Now you don't have to use Eco-Complete or an expensive substrate if you are not planning plants, but look for something that says no affect on pH.
I'm planning a planted tank with Eco-Complete for Angelfish. Eco-Complete says "Will not increase pH or Carbonate hardness in the long term" (http://www.caribsea.com/pages/products/planted_aquar.html). Now you don't have to use Eco-Complete or an expensive substrate if you are not planning plants, but look for something that says no affect on pH.