Bol
Fish Addict
How do I know what my PH is? Is there a test kit for that too?
Yep. To cover all common bases with fish-keeping, you should have tests for pH, KH, ammonia, nitrite, nitrates, and probably GH.
I'd recommend (since you mentioned Petco, and I know they stock these) the Aquarium Pharmaceuticals Master Test Kit (comes in a long green box, about the size of a very small loaf of bread). As usual with most "dry goods" that Petco carries, it's usually a ton cheaper online.