What happened to my neon tetras? They became diseased just after my plecostomus had problems ...?

I have a 55gal tank with 2 neon tetra, 1 black mollie, 1 silver mollie, 3 glofish, and 1 plecostomus. Long story I had to clean my tank completely because I found my plecostomus swimming upside down and in cirlces. I got him out thinking he was going to die, algea had build up so I removed them all. After setting the tank up my 2 neon fish were almost completely white. Research online leads me to believe they have pleistophora, caused by sporozoan. However the ways it says my tetras could have got this make no sense for my fish. I had no dead fish in my tank and I do not feed them live food. I feed flake food and freeze dried bloodworms. Could the freeze dried have the same effect as a live? And other than watching them and checking nitrates and all that how can I make sure my other fish won't contract this?