I have had a 10 gal. tank for about 2 months now, all my nitrate levels are correct and I had a dwarf gourami die, then 2 days later my male swordtail died, and now my only platy is looking like he is on his last fin. They all kind of floated near the bottom and stopped eating. The rest of the fish are acting normal. I do weekly 25% water changes and I siphon the gravel every 2 weeks. I have no live plants and my temp stays around 82ºF. Could the first death caused the rest of them? I have left: 1 Platy 3 Zebra Danio's 1 Female Swordtail 2 Cory Cats If anyone can help I would greatly appreciate it.