pH swing and gas exchange question.

[3_high_low]

Hi Randy,

My pH ranges from 7.85 at night to 8.2 in the afternoon. (If I don't drip limewater at night.) How would you rate that as far as a gas exchange indicator?

Also, I'm hooking up a Myreef becket injector skimmer tonight. Do you think that might help keep the pH up at all? If this skimmer cranks out as much skum as I expect I might just run it at night.

Thanks!

[Randy Holmes-Farley]

3-high:

<< My pH ranges from 7.85 at night to 8.2 in the afternoon. (If I don't drip limewater at night.) How would you rate that as far as a gas exchange indicator? >>

I'd say that is on the low end of average. I was thinking about this just now because of the gas exchange post in the main forum.

IMO, I'd say that

0.1 pH swing or less was very good
0.1 to 0.2 was good
0.2 to 0.4 was less good
> 0.4 sounds marginal to me

There are a number of qualifications, however:

1. If you do anything different between day and night, like limewater additions, this may mask the limited gas exchange (or make it look worse if you do things backwards).

2. If you have a refugium on an inverse light cycle, that too may mask the gas exchange issue.

With respect to CO2, masking the effect, and actually changing the effect may be one in the same, but if you use pH swing as an indicator of O2 exchange, that may not be the case.

3. The pH swing may be biggger at lower pH simply because seawater at pH 8.4 is more heavily buffered than seawater at pH 8.0 (because carboante provides buffering against downward pH changes, and carbonate is much lower at pH 8 than at 8.4.

[Randy Holmes-Farley]

<< Also, I'm hooking up a Myreef becket injector skimmer tonight. Do you think that might help keep the pH up at all? If this skimmer cranks out as much skum as I expect I might just run it at night. >>


If you are using limewater, it might actually reduce it. Without the limewater, it may well raise it, yes.

I recently stopped my skimmer, as an experiment, and thought I'd see an increase in the pH swing. I did not, but I do have an inverse light cycle refugium. I can't so readily tell the absolute effect that the change had on pH because I titrate the amount of limewater added based on the pH. It wasn't big, however, and if anything, it went up (as expected for a limewater tank).