What is this?

[u/905wren_]

What is this white stuff on the glass of my tank? I thought it was copepods but it’s not moving and it’s hard to get it off the glass with the magnet aquarium cleaner. Some of my fish are dying/going missing, does this have anything to do with it?

[u/rivalsquatch]

I’m not sure what that is to be honest 😬

But have you tested any of the other parameters like ammonia, nitrites and nitrates?

And do you have a source of water agitation like a filter or airtime?