Dude I am getting a little jealous now. lol I have looked at the ph res meters, but I would need two since I have two reserviors. As for the CO2, I just drop it down during the last 10 days. 1200 ppm for the first few days, then down to 800 the last week. I had read that you don't need it at the end, but when I cut it out completely the last two weeks, the plants stalled at the end. I mean they just didn't fatten up much during the last couple of weeks. So, I have been doing it this way the last couple of grows with good results. I guess the idea is that reducing the co2 allows them to ripen.