I've never had an aquarium before and decided to get one to help "liven" up my apartment a bit. I got an 18 gallon tank yesterday and is planning to put in 3 small goldfishes (no more than 2 inches). I have a 20 gallon filter made by top fin in it and i put a thermometer and an ammonia detector in the tank. I've put in two conditioners made by kordon in the tank that should remove any nitrate, nitrite, ammonia, chlorine, chloramines, and detoxifies any heavy metals last night. I did attempt to take care of some fishes when I was little but they all died of funky diseases... at the time I had no idea what it was but now I know some of the things they died of was from ick, fungal growth, and (i forgot the name, but it's where the scales starts sticking out and makes it look like its cold... i just know it's deadly and incurable as soon as those symptoms starts to show). I'm just kind of scared my goldfishes will die from my carelessness and lack of knowledge and I wouldn't want to repeat any of the same mistakes, so... My question are as follows: (1) Is there anything I'm missing for my aquarium? (2) How long should I wait before I go buy my goldfishes? (3) Under gravel filtration system... should i have one? and why? (4) Stress coat solution, when should I put these in? (because i know that fishes get stressed when they are placed in a new environment... should I put the stress stuff in my tank the same day i put my fishes in?) That's all I really want to know for now. I really want to get my fishes NOW but I'm pretty sure it's still too soon and my tank is not in the proper condition to have fishes yet. Any suggestions and or tips for a beginning like me to keep a nice healthy aquarium?