I've been thinking, and I reckon this could be the reason behind the flicking my corydoras have been doing since I got them. Perhaps their slime coat is the issue, and that's why the sand is sticking to them.
I've got a short clip to share for now, but the full version is uploading to Youtube - it's a bit longer, about a couple of minutes.
Corydoras catfish and sand sticking issues
Re: Corydoras catfish and sand sticking issues
It seems like your corydoras are experiencing some issues with excess mucous, likely due to something in the water irritating them. This would explain why the sand and gunk are sticking to them.
You should test your water parameters for ammonia, nitrite, nitrate, and pH to get a better understanding of what's going on. Also, take a clean fish sponge and wipe down the inside of the glass - this'll remove the biofilm that's accumulated, which can harbor all sorts of bacteria, fungus, and other microscopic life forms.
I'd recommend doing a 75% water change and gravel cleaning the substrate daily for the next week. Make sure to dechlorinate any new water before adding it to the tank. If your filter hasn't been cleaned in the last two weeks, now's the time to do it - just be sure to wash the media in a bucket of tank water and reuse it. Don't clean the filter if it's less than six weeks old, though.
You should test your water parameters for ammonia, nitrite, nitrate, and pH to get a better understanding of what's going on. Also, take a clean fish sponge and wipe down the inside of the glass - this'll remove the biofilm that's accumulated, which can harbor all sorts of bacteria, fungus, and other microscopic life forms.
I'd recommend doing a 75% water change and gravel cleaning the substrate daily for the next week. Make sure to dechlorinate any new water before adding it to the tank. If your filter hasn't been cleaned in the last two weeks, now's the time to do it - just be sure to wash the media in a bucket of tank water and reuse it. Don't clean the filter if it's less than six weeks old, though.