Cupramine

[Lfisher]

I've been treating my tank for the last several weeks for gill flukes and despite slowing increasing the concentration, my fish are still 'flashing'. Several ramshorn and apple snails seem unaffected and are even starting to re-produce. I removed the carbon prior to treatment and the last copper test read close to 3.0 mg/L (recommended copper concentration for treating freshwater is 0.25). I'm curious if any of the aquarium decor/media could be absorbing the the copper? Possibly peat??