chocolate tang and powder blue white ich spots come and go.

[ngoodermuth]

I don’t use polylab I personally believe it’s just a management tool it won’t eradicate ich or velvet.

This

And, I do believe your fish has both a very heavy ich infestation, and definitely black ich. I can see the black spots clearly in the first set of photos.

I don’t think it looks like velvet personally, but without seeing it in person it’s hard to say with certainty... some tangs can get so covered in ich that it actually looks like velvet

 

[Scotcheggs]

The Polylab suppresses the Ich while in the free floting stage if i remember correctly.

I personally did not like it and cannot see how it could get rid of velvet or ich from a tank.

If I was in your position I would remove the fish and QT then go fallow for 8 weeks.

What other fish are in the tank ?

 

[Stigigemla]

To me it looks like all three. Ich, black ich and velvet. I would remove the fish from the tank.
As the other fishes dont seem to be infected I dont see any reason to do anything with them. But You cant take the powder blue back in the tank because it will be weak after the treatment.
You can have the tank for years with passive parasites in it but they will attack a sensitive fish or spread in case of a tank crash.

 

[Ashley Kekua]

i do not recommend polyplab no no no, it's company practice is suspect