Just check your tank ph, Ca and dkh for a week or so, to see if you're matching your calcium load. Unless your tank ph drops, there's no reason to raise the effluent ph. If tank ph stays okay, but Ca and Alk are dropping, increase both the CO2 and the effluent drip rate. If your Ca and Alk levels start rising, you can slow down both the effluent drip and CO2 a bit.

But, if your Ca and Alk levels stay more or less okay but your tank ph drops, you'll want to raise the effluent ph a little, but not so much that you see a big drop in effluent dkh. Some reactors, particularly small ones, seem to need to run at a low ph. Also, what are you using for media? ARM supposedly works well at a higher ph than crushed coral, but that's only hear-say, mostly by the manufacturers of ARM. so, if you have a small reactor (say 4lbs of media or less) and are using crushed coral, you may need to stay at 6.6. That's about where I ran my smaller reactor. Really it's fine as long as there's not a slow steady drop in tank ph.