Need some more info.
Size of tank in gallons or litres.
How many fish and which type.
Water stats in ammonia,nitrite,nitrate, and ph.
Where are the patches on the fish.
Do the patches look fluffy or bleached out.
Any redness in the patches like on the outside or centre of the patch.
Tank is 270 litres
Stocking
2 Kribensis Pelvicachromis pulcher
1 Gold Nugget Pleco (L18) Baryancistrus sp
5 Clown Loach Chromobotia macracanthus
2 Dwarf Gourami Colisa lalia
3 Bronze Cory Corydoras aeneus
2 Blue Ram Mikrogeophagus ramirezi
2 Golden Eye Cichlid Nannacara anomala
1 Dwarf suckermouth Otocinclus vittatus
23 Neon Tetra Paracheirodon innesi
10 White cloud mountain minnow Tanichthys albonubes
2 SwordTail Xiphophorus hellerii
1 Platy Xiphophorus maculatus
I'll do some tests tonight and post them - the water is fairly acid
Patches are near the tail and go from top to bottom of fish - not fluffy more bleached out
No redness