Couple of questions on my set up 20 gallon aquarium?

I have had a salt water tank for 3 years now and I don't have a test kit or anything. my fish have not died of that kind of stuff. washing the gravel will not really effect the tank as long as your filter is doing its job. Its also a good idea to talk to somebody at a pet store that sell fish, they generaly have someone that specializes in aquariums.