Green water sucks!

[Psyire]

I've seen this problem corrected by running a higher pH.

[midgetwaiter]

I don't have many ideas about where it's coming from but I bet you could fix it by adding some live rotifers. Your corals would probably like that too.

[Johnny Reefer]

Not that it's necessarily gonna help your greenwater issue, but....I'm pretty sure NitraSorb is for FW only. IMO, you should switch to Nitrate Sponge for SW.

Edit: But then, if your nitrates are undetectable, maybe you don't need any nitrate removing media.

[Nate]

Start running a UV sterilizer, run a low amount of flow through it and it should be gone in three days.

Any chance your caulerpa is going sexual on ya? How does it look? Does it happen after cleanings?