So my CT Zatara has some serious dropsy. I've been gone for 8 days, when I got back he seemed fine but didn't come out of his ornament to eat, but he's done that before so I didn't worry about it. But last night when I went to feed his scales were pine coned out, the worst I've ever seen of dropsy. The tank is 29 gallons. I have two males divided then a large area with Zatara, 6 platies, and 3 ADF. What causes dropsy?
Also before Zatara was with the platies I had one of my VT's in there,the platies nipped at him so I moved him and put in a different VT. He became a tail biter

Now this with Zatara! I've never had a problem with bettas and platies, can someone explain this to me?? Or is it just because they are in such a big area? Thanks.