YoYo loach - upside down and about to die?

[Lexifir]

I have three YoYo loach but one of them seems in a really bad way.
They have been in the tank for about 1.5 years.
Yesterday had a 30% water change and another 25% change today, yet this doesn’t seem to have helped.
This loach is laying on its side, sometimes upside down, driving itself into the ground, sometimes shooting off into the side glass of the tank and doing weird stuff...
The other two appear fine and are too damn fast to photograph!
This issue began two days ago.

Am I looking at a parasite in the tank, some kind of disease or something else... what can I do to fix it?

 

[Lexifir]

The tank is normally fairly clean, I’ve only just finished adding clean water and have cleaned the filter again.... hence I disturbed a bit of loose crap on the ground

 

[Colin_T]

Hi and welcome to the forum

If the fish is laying on its side and sometimes darting off suddenly, and crashing into things, then it either has a bacterial or protozoan infection in the brain. They don't normally recover from this and the best thing is to euthanise it. However, if the fish is still eating, then do big daily water changes and gravel cleans for a couple of weeks and see if it helps.

To prevent other fish from developing the same issue, do a 75% water change and gravel clean the substrate every day for at least 1 week (preferably 2 weeks). Make sure any new water is free of chlorine/ chloramine before it's added to the tank. After that, do a 75% water change and gravel clean once a week.

You should also clean the filter if it hasn't been done in the last 2 weeks. Wash filter materials in a bucket of tank water. Established biological filters should be cleaned at least once a month and every 2 weeks is better.