Chris,
Read up on Asparagopsis taxiformis. What's growing in your tank is the sporophyte generation (It's also available in gametophyte). I believe it concentrates bromine (or is it boron, I always forget) so it tastes yucky to lots of herbivores... HOWEVER lots of gastropods like to eat it. Mexican or Pacific snails of the genus Turbo may be helpful. Is there less lighting on your 'fuge than your main tank? Do you test your water? If so, what are you nitates and phosphates?
GL and HTH,
Kevin