Single white patch at base of caudal fin

Would appreciate any help in diagnosing this. Apologies for the poor photos - best I could do!

I've had this royal gramma for about 3 weeks now. Just noticed this morning a single white spot on the base of its caudal fin. There also appears to be a very small grey patch surrounding it. There are some faint grey roughly circular patches on the head that don't photograph at all.

It's not clear from the pictures but the spot itself is not a dot but a small raised elongated growth maybe 0.5 mm long projecting from the fish's skin which makes me wonder if it's some sort of parasite?

Fish is behaving normally and none of the others appears to be affected (so far at least)

Water parameters Ammonia 0, Nitrite 0, Nitrate 0, Ph 8.2, Phosphate 0.8

Any help on diagnosis and treatment and preventing a recurrance will be gratefully received!

Thanks

NB Sorry, that phosphate should have read "0.08".

Also:

Water changes - 10% weekly

Tankmates - 2 small clownfish, a 6 line wrasse and a long nosed hawkfish

1 toadstool coral and 1 mushroom coral

6 turbo snails

No changes to any of the above since the royal gramma was added. The wrasse did start trying to bully it briefly when first added but I distracted it with a mirror against the glass and they've got along fine ever since.

Not sure if this is still an issue but bigger pictures and more light would help us see things better.

The area could have an injury/ wound and the grey patch around it is excess mucous produced by the fish to protect the damaged tissue.

Thanks (a bit late I know).
You are right about the pictures - still working on that.
Well, anyway, the lesions disappeared and as the fish didn't seem to be having any issues I put it back in the display tank. Was fine for a few days and then vanished. No sign of an ammonia spike but it's been a while now and I'm afraid it must have died. Stress maybe, or perhaps an underlying/opportunistic infection? I guess I'll never know.
It's a pity. I will probably get another basslet as they are spectacular fish but will give it a while to see if anybody else seems to be going down with anything. They all seem fine so far.