Cannot maintain pH

[Wrench]

I'm having a hard time maintaining pH in my system. I had initially assumed that the problem was my Ca rx so I added a second chamber to it to scrub off excess CO2 and I also added a kalk stirrer and an airstone to the sump. Absolutey no help at all. Every 12 hours the pH drops by .3 and will eventually settle at 7.7 if I allow it to. I have been buffering it daily with a kalkwasser slurry but I need to find a more permanent solution.

Ca 390
Alk 4 meq/L
Mg 1300
ORP 390

The system is a 240g display, 75g basment sump, MSX skimmer, RedSea ozonizer, carbon Rx and all top-off water is run through a kalk stirrer.

edit: I should add that I am measuring the pH with an AquaController APEX with freshly calibrated probes

[bdare]

How old is your tank? With you alk at that level either you still have CO2 build up or you have a lot of decay in the tank.

[HighlandReefer]

Usually the problem is high levels of CO2 in the areas where your system are at. The extra CO2 in the house air dissolves in tank water and reduces the pH. The calcium reactor will have a lowering pH effect, perhaps best to run it during the day and run your kalk reactor at night. Gas or Oil appliances near your tank or sump can add additional CO2 to the surrounding air, especially if they are not properly vented.

Randy provides more details in this article:

Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm

[bertoni]

I agree that the problem could be carbon dioxide. There's some chance of measurement problems. We see a lot of those. I'd try aerating a cup of water inside the house for 3 hours or so, and checking the pH. If it rises, the tank might need more aeration. I'd check for surface films and make sure that the skimmer is working well. If the inside aeration test doesn't improve the pH, I'd try aerating a cup of water outside for three hours. If the pH doesn't rise outside, the problem likely is the measurement device.

[Wrench]

Thanks for the replies. I suppose that could be the problem, I will do the test tonight. I'm skeptical because the majority of gas exchange takes place down in my unfinished basement which is where the sump and frag tank are. The basement air is not circulated through the house but is ventilated outdoors. Theoretically the amount of CO2 (exhalants) from people in the house should be minimal in the basement.

Is it possible that the ozone could have an affect on the pH?

[bertoni]

Ozone won't affect the pH directly. It's not the cause of this problem.

[tmz]

You may need to dial back the CO2 level in the reactor and/or up the kalk dosing. Many with reactors run chronically low ph in the 7.8 ranges. 7.7 is low and a concern assuming your measurements are correct.Dosing clear kalk water rather than slurry would likely be helpful and minimize overdosing , precipitation and impurities.