Hello; After some thought I tend to think
duanes
has a sound take. Fish can survive in less than ideal water but leaves them exposed over time. We all may harbor pathogens or become exposed to pathogens which our immune systems fight off successfully until we are stressed. Then when stressed the pathogen can take hold. I have given up keeping some fish which do not do well in my water.
I would still consider a slight uptick in WC if just to see if such a simple tactic can make a difference.
A hospital tank can be a plastic bucket or even a smaller jug of some sort. Makes it less expensive to dose a suitable concentration meds, assuming you have something to try.
A few years ago, I had an infection of cyanobacterial algae in my tanks. The algae which form thick sheets over everything. It was expensive to treat a 55-gallon tank with antibiotics and did not take anyway. I put the fish in five-gallon buckets and the live plants in five-gallon buckets. I treated the plants in the smaller buckets.
I took the 55-gallon tank down to the glass. I washed the gravel to remove the detritus then soaked the gravel in a CLOROX solution in buckets. Also soaked the filters, hoses, nets, heaters and any other equipment which touches tank water in such a solution.
I disinfected the tank. Not sure which method I used. My normal way to clean a tank is to make a wet paste with non-iodine table salt and use a soft cloth to scrub the glass after a thorough rinse. The salt paste will clean the glass without scratching, providing all the gravel bits are gone. I may have also soaked the tank with a Clorox solution.
A key thing is to have something like PRIME to treat the Clorox residue. I rinsed everything but there was still a residue. After setting the tank back up with gravel and equipment and filling with water, I dosed the tank with PRIME. I let the tank run for a few days with heaters & pumps running. I threw in a few snails to see how they faired. When they did not do well, I dosed more PRIME. When snails did well, I tried planting a few live plants. Then a few more snails. Eventually the fish & plants were all back in. Been OK for over ten years now.