Thanks for that info, Richard. I'm going to have to do some investigation based on that. I never did make it out to buy the alk/ca kits today, but I suspect alk will be low. And I can do the aeration test tonight. I doubt it's high CO2, as I don't have a Ca reactor and the water is nicely aerated between the splashdown into the sump and the skimmer, but we'll find out.

Chris