Rotten Egg Smell

Question
My son and I keep a 10 gallon tank of freshwater fish.  He is 10 and has learned how to change out the water and filter, etc with little help from me (he is 10).  Anyway, he/we cleaned out the tank about a week ago.  We replaced about 3 gallons of water, cleaned the gravel, changed the filter, etc.  I am not sure if he added the necessary stabilizing chemicals to the water.  Anyway, I noticed that the water was a little cloudy but did not think much about it.  However, tonight we noticed all of the fish were sluggish and the tank smelled horrible.  Many of the fish had fuzzy white stuff on the bodies and fins.  We tried to add some stability and stress chemicals to the water, but within 10 minutes they were all dead.  So now we have an empty tank of rotten egg water.  What do we do now?  Do we empty the whole thing and start over?  If so, how do we do it?  It has been awhile since we have had a new tank or started from scratch.

Thanks for the help.  My son is very upset.

Answer
Tammy,
Sorry to hear that. Lets get the tank going again. Yes, the best thing to do is to empty the tank and start from scratch. Make sure you clean everything that is going in the tank with very hot water. Do not use soap of any kind. The hot water will kill anything bad in the tanks gravel and filter. You will have to re cycle the tank. All you do is after you clean everything, you put it back into the tank. Fill it with water turn on the filter and heater if you are going to have tropical fish. If you are going to have cold water fish you will not need the heater. You will let this tank run without fish. After a couple days you will start adding fish food to the tank every day. This will bring in the ammonia needed in the cycle process. This will seed it and help the filter cycle. In a couple of days you will see the tank water clouding up. That is the first bacteria bloom. This bloom is the harmful bacteria. After a week or so the second bacteria bloom will set in. This is the good bacteria that the tank needs to keep the fish healthy. You will start testing your water daily at this point. Once the ammonia and nitrites levels are a zero for 5 days straight then you can start adding the fish. The cycle process take between 2 and 5 weeks.