Hi everyone! Im new to fishkeeping and fishlore... so hello! Alright... so my question has to do with my poor dying spotted cory carfish.

He/she is currently laying on his side in my tank, breathing heavily. He has blood at the base of his fins and his belly is very sunken. tankmates are one female platy one albino cory catfish and 12 platy fry. ok, now for the history... i just got him 3 days ago. i dont think the petstore feeds their corys anything special, and suspect that he was really hungry/starving. I have been supplying algae wafers, but just recently found out they dont really eat those... although mine was muching on them. I have a new 10 gallon (well, been up for about 4 weeks) that i am cycling. i didnt learn about fishless cycling until after i got my fish, so my ALBINO cory cat endured (and is still doing well) the first few weeks. so, 3 days ago, i went to the store and bought one female platy (she had 12 babies, one with a bent spine a few hours later0 and my sick spotted cory catfish. Ive had so many problems with the tank.... grr frustrating. lost my first batch of fish (total of 5 balloon mollies and some balloon fry) to
ammonia strikes. I restarted the cycle to clean all the crud out of my gravel and try to get it right, but still had my albino cory left. SInce i have been performing daily 20-30 percent water changes. I also know cory cats need to be in schools but simply dont have room yet. Everyone else seems fine, except the platy is always hiding. Thanks for your help!