Help sick Clarkii Clown

[mdl]

My setup is 6 months old and all water test are good. The problem is the clarkii (the only fish) is gasping and breathing hard. It feeds well and in all other appearances is normal. The LSF indicated it may be a crab type parasite that is living in the gills and I may need to treat with copper. I’m concerned, and I don’t stress the fish any more then I must. Any assistance with this would be appreciated.
Thanks.

 

[crazy bout salt]

its a seven gallon tank? well its really really small first of all what kind of filtration do you use because you will need a good filter to supply enough oxygen in such a small environment for thta fish

 

[mdl]

Prizm skimmer, 5lbs LR, 2+"LS, Temp 78°, Phosphates <0.1, Ammonia 0, Nitrite 0, Nitrate 0, PH 8.3, Alk 2.2, Calcium 400 Specific Gravity 1.024, Doising Kalk + Liquid Calcium, Oxgen 6, Water changes one gal once a week. Add Kent Essential Elements at water change.
Did a two gal water change when fish first started gasping. That was a week ago. Clarkii is active, responsave to out of tank movement, feeds well, stays close to it's home (a portion of LR), but does patrol tank. Other tank mates: 2 red legged Hermits, 1 emerald crad, and several snails. Ther is some plants as well. If you need any more spacific info let me know.