Hi all, My 55gal finished cycling 2 weeks ago. So 8 days ago I added 5 platies. All of them seemed to be doing well: their colors were getting brighter, the fins weren't clamped, they ate well. Last night, one of them was acting weird. She was swimming slower than usual and staying toward the bottom and it looked like something was wrong with her mouth. I wasn't sure if she was just holding her mouth open or if she got injured some how. I looked up mouth rot but it didn't look like that to me. Her colors were bright and her scales looked normal, no discoloration fom what i could tell but she died today. My water readings: Ammonia - 0 Nitrite - 0 Nitrate - 5 Feeding a variety of omega flakes, bloodworms, shrimp pellets, and a little bit of spirulina flakes. Any help is welcome. Kinda bummed that this happened. The other fish are acting fine and look fine, but now I'm worried about them.