I've never heard of Yellow Fin Cichlids. The only Cichlid that I know of that has a blue body and yellow fins is an Acei. Then again, there are many fish that I don't know of, but they seem to be the more popular.
A good master test kit is Aquarium Pharmacuticals. If you purchase them from the
lfs, you are looking at at least $30. Big Al sells them for $20 and that's after shipping and tax. Just make sure that it tests for Ammonia, Nitrite, Nitrate, and pH. Depending on if you are going to be keeping plants, you probably won't need one of those massive test kits that has like 30 bottles of solution.
Since I don't know what type of fish you currently have in the tank, I can't really comment on what you should add. But in regards to plecos, A rubbermouth is a great option. They are SOOOO cute and stay small. I have one in my 29
gal right now and everytime I see him I just smile cause he's so adorable. He's so tiny yet he stands his ground against all the other fish. In regards to the snowball, I think they are also VERY cute. In fact, I've wanted to get one for so long but never bought one. They are about $60 around here. It would also be a pretty good option for you. Until you can
ID your current cichlids, I wouldn't add anything else other than the pleco. Most cichlids get pretty big. Unless you are going to upgrade to a larger tank, I'd stay with your current stock plus a pleco.
