New here - and I'm seeking help
We added a sucking loach to our new freshwater aquarium two months ago.
After about a month, it developed a yellow tinge around its gill.
This discolouration then began to spread around the gill area and on to its spine.
I have shown a picture to a few local fish specialists who said they have never seen anything like it before (although one suggested it may be a bacterial problem caused by an ammonia burn).
None of the other fish (a gold sucking loach and two chocolate orandas, alongside apple snails) show similar symptoms. We had the water tested and there's no problems with ammonia, nitrates or ph level.
I have attached a picture. I would welcome any suggestions.