Sick Loach advice needed

[Dragana]

I have a two years old Clown loach, and I've noticed that it has some white matter on fins and on the body. I suspect fungi or maybe bacterial fin infection. It doesn't eat, though it reacts to food, but probably due to mouth infection it can't eat.
I have Sera's Bactopur and Mycopur, but I haven't used either yet, because I don't know how effective they are.
Also, I wonder whether to treat it in isolation or in aquarium, which dosage to use, and for how long? Will I have to change the water and when?
If there are optional ways of making my little friend recover, please do tell!

Thanks!

[chefkeith]

You should use the antibiotics in a quarantine tank.

The water parameters of the quarantine tank should match the main tank. Water changes need to be done slowly. Sick and recovering fish do not acclimate well to changes.

Treatments usually last 1 week, but usually no longer than 2.

[Diana]

Can you tell us more about the tank? What are the results of the latest water tests?
Ammonia
Nitrite
Nitrate
pH
GH
KH
other...

Loaches (and most other fish) can get bacteria infections, and this may show as grey or white on the skin. Fungus is less common, and usually associated with an injury. The fungus invades the dead tissue at the site of the injury.

Many fish will shed some slime coat when the water chemistry is an irritant, for example high ammonia or wrong pH. Loaches seem to do this rather easily, and the shedding slime coat may look like white, or not really white, strings streaming off the fish.

General care for a sick fish includes doing water changes as needed to correct whatever issues may be going on, and to remove as much of the infectious agent as possible, and feeding a good rotation of food. If the fish is reluctant to eat try adding some crushed garlic to the food. For some reason garlic seems to make the fish eat the food.

If it does seem to be bacterial then medicating the fish in a quarantine tank is better than treating the main tank. Some medicines can kill the nitrifying bacteria, and fish that are not sick should not be exposed to meds they do not need.