Harequin Problem

[Tobie]

I have a fairly old harlequin that skin is going a whitish colour and I am not sure what it is or what to do about it. The other harlequin in the tank looks healthy but keeps chasing the fish with the whitish colouring. Both harlequins are the same age. I have platies, tetra and two bristlenoses and they look healthy. Can some one help please.

 

[WILDER]

How many gallons is the tank.
Water stats in ammonia, nitrite, nitrate, and ph.

Any signs of flicking and rubbing.
Excess mucas.
Darting.
Laboured breathing.
Laying to side on the substrate, or leaning to oneside, or resting on plants.
Does the white on the fish look like bleaching beneath the skin.
Do the gills look pale with excess mucas or red and inflamed.
Any patches of cotton wool on the fish.
is the fish fins clamped to its body.
Any red streaking or sores on the fish body.

Do you have neon tetra. If so check the red stripe area still vibrant red and not bleached out.