PH Observations

tjbuege

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Jun 25, 2009
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Being the curious type that I am, I decided to monitor PH levels in my two CO2-enriched tanks yesterday. I know we can't really determing CO2 content based on PH, but that wasn't my goal. I was simply curious to see how much the PH changed throughout the day. Both tanks use tap water, EI, CO2 (from the same 20lb canister complete with manifold and a bubble counter per tank). KH is 3dH and GH is 8-9 dH, for both tanks. CO2 comes on at noon, lights on at 1pm, CO2 off at 8pm, and lights off at 9pm. Here's what I found:

Code:
       -- PH --
Time   20g  29g  Comments
-----  ---  ---  --------
11:00  7.6  7.6
12:00            CO2 On
13:00  6.6  6.8  Lights On
15:00  6.4  6.6
17:00  6.2  6.4
20:00  6.0  6.4  CO2 Off
21:00            Lights Off
23:00  6.8  7.0

I found it interesting that the PH dropped so quickly after the CO2 came on. Is that an indication of anything useful? It probably depends on circulation of water, where I took the water sample, etc. I think the tank has fairly good water circulation. I use a power filter (Penguin? I think 180GPH) for the 20g and an Eclipse 3 Hood system (250GPH) for the 29g. They both also have a MaxiJet 600 powerhead, dispersing the CO2 via impeller. Both have 65watt CFL, although the 29g Eclipse hood uses a retrofit kit, so the lamp is VERY close to the water surface, maybe 1-2". Too close, I know (I have the algae to prove it!) The entire 29g is going to be replaced soon anyhow. 20g uses a Coralife fixture suspended about 6" above the water, open top on tank.

I guess I'm wondering if I can determine whether I have good CO2 based on this particular PH swing? Plants and fish health are best indicators, I know. If nothing can really be gained by knowing PH, so be it. I still found it an interesting experiment.
 

dutchy

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Jul 6, 2009
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I don't think you can determine good CO2 that way, but it sure tells you that is has enough capacity to do the job. If the system would be low on capacity, you wouldn't reach the desired level in an hour. also the pH would rise again if the capacity was insufficient.
 

dutchy

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Jul 6, 2009
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With capacity I mean how much the pH drop is over a certain amount of time. Being able to get to the desired level within 1 hour after lights on seems to be a good average.