I'll admit right now, it was a stupid mistake but I added 3 guppies from the pet store to my tank. I had purchased from this store before with no problems. I didn't add their water to my tank, I netted the fish in. Anyways, those 3 and 12 other guppies have died. My tank has been running for 2 years without adding any fish. The guppies would breed and they'd grow up. I decided to add new blood to the tank. Bad idea. The symptoms are clamped fins and a shaking and rolling of their body. I've done several water changes to fix the issue. I've treated for protozoan parasites thinking that was the issue. Nothing fixed. This has been going on for 2 weeks. I'd lose 1 a day, and up until 3 days ago, 3 sometimes 4 a day. I'd have some days where none died but looked horrible. Today removed any that showed any ill symptoms. The ones that looked fine are staying but still being treated. The ill ones went to a 7.5 and will die tomorrow or tonight, based on the pattern. I've tried aquarium salt. Water parameters Ammonia:0 Nitrite:0 Nitrate:2ppm Ph:8.2 F°:77 Hardness: 8 Haven't changed my water source or anything. Nitrates are low from the constant water changes.