What is this?

I ended up having to use erythromycin. I tried everything and could not get rid of it. It comes back so fast that it will cover everything in a couple of days. I really wish you luck.
 
A couple of weeks to make sure it is all gone.
 
How long has you tank been cycled? I would add a lot more plants to use up the nutrients available in the tank to help fight the algae. If not... you could always try and OD with Excel but your shrimps might not make it through the process if you do the chemical route.
 
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