Yep, all that photosynthesis of the algae is raising the ph, if it's really at 8.4. Unless you have a decent probe and calibration fluid you don;t really know what the ph is.

I disagree with the clam idea. Those are not easy animals to keep healthy, and PC lighting is not good for them. I understand the theory here, I just don't think it's appropriate in this case. Who knows what the Ca/Alk situation is in this tank...Why don't you change ALOT of water, like 50% every week a few times in a row, using good R.O. water and quality salt, keep the lights on a normal cycle, take Larry's suggestion with the macro, and let it go for a while. It looks like there's hardly anything in your tank, BTW, unless I'm not seeing rocks behind the green. Once your water clears up a little, add some more CURED live rock, maybe even put in a nice sand bed and try to get a few filter feeders growing. From the looks of your sump, you hardly have any space for caulerpa, so I doubt if it's having much impact on your main tank. It also looks like the caulerpa gets pounded by your tank drain; is it possible some it is getting passed through the pump? If so, you'll have a "nice" caulerpa patch taking over your tank someday. Oh yeah, you might want to make sure your water is moving enough in the main tank. Just toss a couple of maxijets in there. (Not an actual toss, I'm sure you know!)

Have fun! :grin: