Probably not a quarantine problem.ich and epistylis are both present on almost all fish in aquarium trade. Fish with robust immune systems just fight it off without a problem. Too much bacteria in the water overtaxes immune system and fish starts showing symptoms. Epi in particular does not feed off the fish, it feeds off bacteria in water. If the fish respond to antibiotics you know it's epi.

Successful nitrogen cycle is low hanging fruit. Bacteria free water requires a 10x increase in biofiltration above and beyond ammonia conversion. I still believe this is a filtration issue.

To give you an idea of how truly I believe this... I just set up a 20 long. It houses a single dwarf gouramie. I use a canister filter rated for a 75 gallon aquarium. Overfilter MASSIVELY and fishkeeping becomes very easy.