the issue is, theres no filter. without a filter, not only will nothing fitlter the water, but you wont ever get a cycle going. in order to get a cycle, and keep your fish and soon fry healthy, you NEED a filter.
EDIT TO ADD: the filter is far more important then the heater. especially now in the summer ( not saying dont use a hater, just a filter is much more important for many reasons)
we arent tryig to be hard on you, please dont take it that way, i would read up on the nitrogen cycle asap, and possible re home the fish until you can provide a proper living enviornment they need. best of luck
EDIT TO ADD: im new the the hobby, so trust me, i have made an abundance of mistakes!! but this is a great place to learn. there will ALWAYS be folks anywhere you go, critisize you, but far more folks are genuanly here to help and learn. so try not to get to frusterated when ppl come at you funny, it wont happen much, but WILL happen. keep your head in the game, and soon enough, you will be giving your assistance for others
EDIT #2 LOL: ALL THE ADVICE GIVING THUS FAR IS ACCURATE AND VERY IMPORTANT LOL
I do know about the nitrogen cycle, and I plan on returning the platies back to their 20 gallon home as soon as possible. I’ve been trying to do water changes as best I can. I really hastily put together this tank, and I didn’t think they’d be in there so long. The fry will all be given away, and the tank won’t even have fish in again. After this, it will just be a home for my baby Leopard Gecko until she big enough for a bigger home