Loaches Online Forum

I bought new fish a few months ago and they all died after a few days. their skin became discoloured at a small point on each and then spread across the fish rapidly. before I bought these fish no fish had died in my tank for years. I tested the water after this incident and found the ammonia to be a little high. after water changes and different treatments the ammonia finally got back to 0. I then bought some new fish on Saturday (before which I checked the water parameters which all came out normal) however now the same thing is happening to the new fish. what could be the cause I think the discoloured patch of skin is the slime coat being lost but what could be the cause of this in the first place.
any help would be greatly appreciated.

Do some research, and look up the disease Costia. I think it is actually a parasite.

Other than that, fish will shed their slime coat in response to irritants in the water.
Salt, Ammonia, wrong pH and other things.
Some Slime Coat Enhancers that are incorporated in water treatments actually cause problems like this: One way they 'enhance' slime coat growth is by adding an irritant to the water.

AHA! Costia.

Well now I know what has very neatly killed off all my kuhlii's and striata's.
Now I know what it is I can kill it off.
Oh I'm going to enjoy wachting this parasite die off

Thanks