why low pH?

[johara]

I thought I understood that if both calcium and alkalinity are in normal range, then pH should also be unless CO2 is an issue. My KH is quite stable between 11-13, currently 12, calcium is currentlly 430, achieved with Tech CB 2 part solution and supplemental Seachem reef advantage calcium and marine buffer as needed to keep KH >11 and calcium>380. My pH as measured by frequently calibrated pinpoint moniter is 7.85 at night, rarely above 8.00 in daytime (except for an hour or so after adding the buffer). No calcium reactor, no kalk. I tried raising the KH even further with the marine buffer but couldn't sustain a pH of 8.2 without levels so high the calcium precipitated out down to levels in the high 200's. Not an option with SPS and clams in the tank.

After researching it sounded like CO2 buildup might be an issue, though it didn't seem likely as I have a skimmer going 24/7 and a fair amount of surface agitation. I tried putting an airstone in a cup of tankwater for an hour or so - there was a small change in pH from 7.99 to 8.04. Any ideas?

Thanks,
Johara

[Randy Holmes-Farley]

Johara:

<< After researching it sounded like CO2 buildup might be an issue>>

It still might be, but in this case it may be building up in the room or home. FWIW, CO2 can become substantially elevated in homes, especially new, tight ones. It's not a problem in my case where I can feel the wind whistling around 93 year old windows, but others are not so lucky!

In fact, a friend of mine had such an issue that he got a CO2 detector (not cheap) and found greatly increased CO2 compared to outside air. He resolved the problem by opening a basement window for better circulation around the sump, and found that the pH rose. I think building engineers are allowed to let CO2 build up to at least double normal levels before taking specific actions, so it can build up a lot.

[johara]

Thanks for the quick reply! Sounds like a difficult problem to remedy, at least in winter. I'll see if I can rig something up to bring air into the skimmer from outside and see if that changes the pH. Assuming high indoor CO2 levels is the culprit, how quickly should I see a change if I feed outdoor air into the skimmer?

Johara

[Randy Holmes-Farley]

You might try the same bubbler test on outside air before going about changing the main system. If you do have a CO2 problem and bring in low CO2 air, the effect should be noticed in a day or two.

Another possiblity is that the pH testing is off somehow....

[johara]

After only about fifteen minutes of bubbling tank water outside the pH is 8.15 and rising (inside tank water still 7.99). That also explains why I didn't have any pH problems in my old (leaky windowed) house. The pinpoint monitor purchase coincided with the move, so I just figured the old chemical test kits must have over-read the pH. Okay, so I could drill a hole in the wall for air input to the skimmer, but how about the rest of us non-fish folks? Guess human health effects of high CO2 isn't really your realm, but I do wonder. The tank is in the family room where all five of us and the dog frequently hang out in the evening - and this is a well sealed new house.

And back on the fish side of things, even if I input outdoor air into the Berlin skimmer, will that be counteracted by the open tank surface area (11x48") still in contact with high CO2 levels?

Thanks so much for all the info!

Johara

[Randy Holmes-Farley]

Johara:

I'm glad were tracking the problem down!

As you suggested, I'm not an expert on human health (though my job is the vice president of chemical research at a pharmaceutical company). Here's what I see in the Material Saferty Data Sheet for CO2:

OSHA limits for 8 hour/day exposures are about 14x normal air (5000 ppm).

At about 85-100 times natural levels the human response is increased respiration and headache. At higher levels you add nausea, vomiting and unconsciousness. Higher still (400x normal air) can lead to death.

That said, it only takes a small amount of CO2 to drop the pH in a reef tank. A doubling of CO2 will significantly drop the pH. A ten fold increase in CO2 would have the pH down in the low 7's for the same alkalinity.

Consequently, I wouldn't take a measured tank effect as sign of potential toxicity. Still, if you have unexplained headaches (or heavy breathing), more fresh air might be in order.

[johara]

Sounds like we're not in imminent danger of much more than a few extra yawns. I'll ask my buddy in the environmental health dept to see if she can borrow a CO2 monitor just for fun.

Thanks again for the help. Off to my drafty work place now - maybe I should have a tank there!

Johara

[Randy Holmes-Farley]

If you can get a hold of one, that would be interesting. If you get any numbers, let us know what you find!

[Lunchbucket]

maybe this explains my constant 8.0pH now. i will try cracking a window and seeing.

thanks
Lunchbucket