Bubble algae (red) how to eliminate/control?

[JPotter]

I have a BC 29 that has been up for about a year. In the past weeks the nitrates increased (I think as a result of feeding a new tubastrea). I have cut back the feeding (I hope it doesn't starve) and have done several 5 gal H2O water changes. The nitrates have improved but are still high. I am also adding an "anti nitrate" product that I think is similar to using vodka and/or vinegar.

There has always been the old bit of red algae but recently it is creeping all over the live rock, power heads and onto the base of some corals (I have no SPS).

My lights are PC fluorescents on for 12 hours. The corals generally seem content and the Clown fish carry on. The 6 line disappears for a few days every time I do a water change (I hope appears again soon).

My question is how to control the already existing algae? Some suggest emerald crabs (I have hermit crabs and 1 small porcelain crab). Do they work? Are they reef, fish and invert safe?

Can I do more drastic water changes without killing things (I use Ro water, set temp and salinity and mix it 24 hours before use). If so what regime is suggested?

How little can I feed to lower the nitrates without compromising the inhabitants?

Thanks for any and all help with this. My tank now looks like the rocks are purple (coraline algae) and red (bubble algae).