If there is algae .
I know there has to be high
1) nitrates
2) phosphates
Algae needs these high nutrients to grow .
Is it diatoms or cyano bacteria ?
Cyano is normally red .
But can be any colour ,
It's a slime algae .
Diatoms are normally a rusty colour .
For the nem , you have one of the easiest and hardiest to keep so I'm not worried .
A rule of thumb for reef keeping though ,
A nem should only be kept in mature systems ( 1 year plus )
You have a better chance of success keeping it alive , and thriving . Do you have any pictures ? Of the algae and anemone ?