I have never had such a problem with tanks and fish as i have with this new tank we set up for my 2 year old. Its a 20 gallon tall and was given to us by a friend. We set it up right after xmas with 2 black molly's and male fancy guppies. The guppies died within the first 3 days and the mollys were doing well. I took my daughter after her docs appt a week ago and got her a few new fish for doing such a good job. We got home floated the new fish and released them when to my horror i noticed that one of the mollys was showing signs of ich. Of course it was too late i had already added the new fish. I began treatment of the tank right away but all still died ... even the mollys but they were the last to go. We took the entire tank apart cleaned everything well took out the gravel and put new in fresh from the bags. I let it cycle for almost 2 days and got her new male guppies. I got 6 as they were "on sale" and i figured if they didnt make it it wouldnt be such a big monitary loss. Well 1 day later i had 4 dead out of 6. I took them to the store and had them replaced and of course being a dinkus like i am took the fish in the same container as the water so they would not test it. I brought home the 4 new fish and floated them then released them and when we put our daughter to bed last night they were all huddled together in a corner of the tank. I have had many many fish in my life but never an issue with fish falling like flies before. It almost seems like they are cold but my thermometer reads between 78 and 82. I know there is no more ich because of everythign being cleaned and steralized. ( i souaked them in boiling water for 30 minutes) Can someone help me?

First.. welcome to kokos

The cycle takes at least two weeks to complete and after the 3 day mark ammoina starts to get pretty high and toxic, instead of confusing you with my explanation.. heres a link about cycling http://www.kokosgoldfish.com/cycle.html this ones cycling with fish (its goldfish but its pretty much the same) and at the bottom theres a fishless cycling link.
Not having a full cycle is probably the reason the fish died.
Do you have test kits? if not they are pretty important, and since you still have fish left you are really going to need them asap to monitor the water as it cycles.

yea what lucy said it's probably the cycle process that's killing them or you got them with some kind of illness. if you do a cycle with fish (it's best to do it fishless), i'd recommend getting amquel or prime to treat the water during the process since it's suppose to bind ammonia to where it won't hurt the fish and also aquarium salt cause i think it's suppose to help during the nitrite part, but only use it if you have fish that can tolerate salt. i cycled my tank with my fish and they all came through it fine and right now they are going through it again since i had to treat my tank with meds so my cycle crashed and they all seem to be doing good so far.

also when you get new fish you really shouldn't just dump them in with your current fish cause if they are sick then your healthy fish can catch it and die as well. you should quarantine them for at least two - four weeks.

Good advice everyone I just have a couple more things to add.

You should slowly acclimate any new fish to the new water conditions of your water, especially temperature and pH. A pH shock can kill fish pretty fast.

When you say you sterylized the tank really well, what did you use? You mentioned boiling...what things did you boil?

For future reference, you should rinse all new gravel before placing it in the tank. I don't think this is the cause of your fish deaths though, unless the tank water is the same color as the new gravel

OHHHH i did rinse my gravel .. very well i might add. I poured boiling water over my filter and all its parts and the fake plants and the little nick nacks in the tank. I wiped the sides of the tank well with really hot water (burnt myself). As i have stated i've had many aquariums in my life .. everything from a gold fish bowl to a few monsterous 100+ gallon tanks. Never in my life have i had this problem. I think the tank just doesnt like me. Thanks for all the suggestions though.

Although your method may have worked its probably best to boil rocks and hard ornaments for 10 minutes in a rolling boil; toss any soft media like cartridges, and sponges; and run the tank with empty filter and other stuff with a Potassium permanganate solution or a bleach solution, then rinse very very well (and for the PP use hydrogen peroxide too). Pretty much nothing gets past that

My guess is that either the fish are sick when you get them, they are stressed by a pH change or something similar, or the high ammonia. I'd buy a test kit so you can acclimate your next fish better, as well as keep track of ammonia and nitrite until you are cycled. Sometimes there is just a lot of bad luck. I have horrible luck with goldfish

Good luck! *fingers crossed*

you have a water conditioner/dechlorinator, right? i've heard of fish dying from cycling, but they usually make it more than one night. when i very first started w/ aquariums i lost two tetras cuz of cycling and cold water, but they lived a good 4 or 5 days before they passed.

also, is your water constantly 78-82? even tho mollys and guppys can take a little cooler water; without a heater in the aquarium, temperature can fluctuate a lot, even if the temperature in your home doesn't seem to.