That is not red slime...cyanobacteria.
It is an algae referred to as cotton candy algae ~Asparagopsis.
It is very tough to get rid of...
I have the same stuff in my refugium.I am working on outcompeting it with chaetomorpha.I have been reading about people who have used a bunch of mexican turbos to eat it,and supposedly margarita snails will,but the latter will not live long in our tanks.Keep water quality high with water changes.It is growing from high nutrients.