all my fish are dying!

Question
I have recently set up a 20 gal tank.  I set it up a week before I bought the fish.  we had an alga eater(sucker fish) a snail, small crab, two angelfish, five long fin tetra, a guppy that survived the last tank crash and two Mollies, white and orange.  So far, the sucker fish, the crab then one angelfish died.  The kids may be over feeding the fish, the water is a bit cloudy.   I keep the water at 79 degrees FL. I also feed them the flake food.  I had been dropping alga discs for the sucker fish but no one seemed to care for them but the guppy.  I have kept the pH in safe to ideal ranges.  I am not so sure what I am doing, or not doing to keep this tank healthy.  Please help.  I don't want to kill my poor little friends anymore and I need more wisdom to keep them alive.  Everyone is sluggish.  I just changed out two gallons of water using reverse osmosis filtered water.  

Thanks,Susan

Answer
Susan,

Your aquarium is suffering from new tank syndrome, you put way to many fish in to fast, in order for an aquarium to be able to support its inhabitants that tank needs to go through the nitrogen cycle and develop a bacteria culture that can deal with the waste that the fish put off so that the closed environment of an aquarium doesn't become toxic.

Your fish are dying because they are being poisoned with ammonia, at this point it might be to late to save them but a few things you can try are, 30 water changes every other day for about 7 days, lower the temperature to around 75F and add some aquarium salt, 1 teaspoon per 2 gallons to bolster the fish slime coat helping them to be more resistant to a poor environment. Get a good test kit to keep an eye on ammonia levels.

Good luck,
Craig.