White Spot i think

[ClairePass]

I have a black mollie in my fish tank and every couple of day he gets covered in what looks like speaks of white dust (its really hard to describe its not cottom wool balls, as its flat and not tiny grains of sand). After reading up about it i thought it might be white spot but after visiting the fish shop the bloke there said it was unlikely to be as it keeps disappearing for a few days then coming back again and also because none of my other fish seem to be affected. Also my black mollie doesn't seem bothered by it. I have never seen him rubbing against anything, he ain't of his food and is as lively as ever. We have tried white spot control medicine and that hasn't done anything. Any ideas? Been going on now for about 1-2 months

 

[WILDER]

If you have no scaless fish in the tank you could try some salt to see if that helps.

 

[ClairePass]

I have 6 very small guppys baby ones about 6 months old and a small loach. Should they be ok.

 

[WILDER]

Don't add the salt with the loach, instead try a salt dip on the affected fish.
http/ukdiscus.com/ken_thomson_salt.htm