Yes, the ammonia, nitrite and nitrate are your most important. The API liquid test kit is probably the best way to go - it also includes pH testing, but that is not as important in your case (or mine). The cheapest I have seen the kit is $23 I believe. Petco has it on-line cheaper than in the store, but you need to pay shipping unless there are some other things you need - they have deals on shipping. It comes out of CA very quickly. There may be other places also. The problem I found with buying the chemicals piece by piece is it costs a lot more. I am going to guess if you buy all three separately they will cost between $25 and $30, but you can check.