what's this stuff?

[sedatedgenius]

ive got this really strange algae (atleast i think it is) growing on my sanbed, it doesnt grow anywhere else at it seems to sprout runners into the sand...

anyone know what this is? its not hair algae, i know that for sure...

 

[JGoslee]

Looks like dinoflagellates

 

[john rochon]

that is dinoflagellates. your in for a battle like no other. sorry to scare you but I've been fighting that in my 500g tank for over 6 months!!!! its ruthless. do a search here for that and follow some of the advice. heres what I suggest even though I'm still having issues.
SKIM
CARBON
REDUCE LIGHTS
REDUCE FEEDING [if over feeding]
SYPHON scum as much as possible [while doing water changes]
RO/DI water [make sure you filters are up to par]
KEEP ALK UP!!
SCRUB ROCK WITH TOOTH BRUSH.
INCREASE FLOW [if low]