Help pls, fish suffering from recurring problem, not sure what to do!

[Jay Hemdal Verified Community Expert]

I guess I should collect all my thoughts before posting. I'm also going to test the water using an ICP from Fauna Marin. I knwo this is geared to reefs but I figure it will tell me if there's some other toxin in the water.

ICP only alert you to elements that are out of balance. The only toxins they identify are heavy metals. All organic toxins are just reports as "carbon".

That microscope may have too high of a magnification. You want something on the order of 40 to 80x magnification. You may get this to work on its lower settings.

To do a skin scrape, you first must be able to capture the fish without causing it harm (not always possible). Then, while it is still in the net, drag a blunt knife head to tail down the fish and try to capture some mucus. Some fish; tangs and triggers, have ctenoid scales with no mucus, so they are difficult to scrape.

Then, add a drop of seawater to the mucus and look at it under the scope - watch for anything moving.