Help?

Question
So i got four fish id say...About three months ago,But now's the time that things are going wrong.I got a Bala Shark fish,A Danio,And a fruit tetra,And then to keep the tank clean a sucker fish(I don't know what the name was)First my danio died after i accidently left the heater off:(Then...A week ago my Sucker Fish died.And yesterday my Bala died.....I have no idea why everything seemed fine.Good temperature,the filter was on....The other fish seemed fine.And i didn't mention we then got another sucker fish.
And now today my tetra is acting sick!We thought she was dead at first.She was stuck behind the filter in my tank.We let her out and then five minutes later she we being sucked up by the filter!,I shut it off and she came floating up to the top.She wasn't dead either.She was still moving a little bit.And then i emailed you.And i just read that bala shark fish need to be in a big tank!(55g or more!And guess what?!
Mine is 2 gallons!I don't know what the people were thinking!They said that theses fish would be fine in our tank!Tina i need your help!If i can't save my fish in time then i want to be able to save my other one!

Answer
Savannah,                                                    Your tank isn't big enough for more than a couple female bettas or a male and maybe a snail and an African dwarf frog. All of which don't need a heater.  Anyway... These tropical fish you have need to be sustained at 76 to 78 degrees and need room to swim especially your bala.If your sucker is a pleco he is going to get huge, they outgrow 10 gallon tanks. These guys need an ecosystem. A tank that is not fully broke down and is just siphoned once a month with a filter carbon change. If you are going to keep tropicals you need at least a ten gallon with a heater that remains on always and goes on and off itself to maintain the temperature after you set it. You wouldn't do more than a 50% water change. They need a bacteria bed in the rocks to eat their waste byproducts. You would never wash it out. Go get a bigger tank and get it set up as soon as possible. Though I think it is probably to late for you little guy .. sorry  Good Luck, Tina