Hi everyone! I am a fairly new aquarium owner as I wanted something interesting for my kids homeschool room. So we got a 20gallon tank and set it up about a month ago. It has several java ferns (5 I think) and about 3 smaller plants up front. We also have a pirate ship thing for them to hide in. I bought a betta when we got the tank (the lady at the fish store said it was fine to put him in early) and then about a week later we got 3 serpae tetras and some sort of betta ball plant. Everyone was getting along and doing well until this weekend. We added a few ghost shrimp and a couple snails which don’t seem to be causing any issue. I also added 3 guppies-2 were dead before the next morning and 1 I cannot find. I suspected that my betta had killed/eaten it.I went back to the store today and they suggested getting some platties instead bc they were a little meatier and may not get picked on by the others. So I brought them home and added them. But then I noticed that my bettas fins were looking pretty ragged and chewed up and he was having a hard time swimming. Researching further I found out that serpaes can become aggressive and should not be housed with “fish that have flowing fins”. I currently have my betta in an isolation tank and am hoping that he recovers. But I don’t know what to do moving forward. Should I get him his own tank? Should I return the serpaes? Any thoughts or suggestions would be greatly appreciated as well as helpful sites or recommended reading.