Around 3 days ago I noticed my platy has a clamped tail/claudal fin. He doesn't move much and usually lays on the gravel. He is also lethargic now and didn't really eat. When he does swim it's not the best looking, he tries to move his whole body( probably because his tail fin is clamped). Parameters are good 0ppm ammonia, 0ppm nitrite and 5-10ppm nitrate. He is a 20g tank with 2 female Platys 3 gourami and 10 neon tetras. In fact he's a expecting dad. Don't wanna see him die. Here are some pictures to help identify the disease. He also doesn't lay on the gravel he kind of tilts down too. I think it's fin rot.