[Delphinus]

Does anyone in Calgary have a UV sterilizer Alan can borrow?

Bob has also suggested a diatomaceous earth filter. These filter out anything larger than 1 micron (if I remember correctly?)

The one profound thought I have is this. There really is no difference (to my eye anyways) in the pictures taken six weeks apart. This suggests to me that the phyto, or whatever it is, is somehow feeding off something. If they weren't, eventually there would be a crest and subsequent population die-off. Instead we see a more or less constant population.

So, what could feed phyto? I thought pretty much that phyto/green water is pretty much completely photosynthetic (I could be way off base here). So, my first questions, what lights are you using, how old are they, and does your tank have any direct sunlight exposure? (I know you said you've cut back on photoperiod, but I am fishing for ideas here.)

Is there a specific thing that you can remember, that before which, there was no green water, but afterwards, there was?

Have you increased, or have you considered increasing, the light over your caulerpa refugium? If you can perhaps get the caulerpa to grow fast, perhaps they can eventually outcompete the phyto for whatever nutrients that are feeding them?