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winland
11/01/2008, 10:47 AM
With the days getting shorter and the sun lower in the sky, the sunlight is coming in my window and directly hitting one end of my 90 tank. It just happens to be the same end that I normally leave my pH monitor probe in. During the early afternoon when the sunlight is hitting my tank, the pH can go from 8.25 up to 8.6 very quickly, sometimes even a bit higher. This pH spike is very localized to that end of the tank. If I put the probe at the other end of the tank or in the sump, the pH readings are much closer to "normal".
It just seems odd / strange that pH can be that much different in a 6' long tank. 8.6 at one end and 8.3 at the other end.

If I put a cover between the window and the tank, the pH drops rather quickly back to normal.

Just an my observations.

winland

Randy Holmes-Farley
11/01/2008, 11:37 AM
This pH spike is very localized to that end of the tank. If I put the probe at the other end of the tank or in the sump, the pH readings are much closer to "normal".

If the pH is localized and you get different answers in the bulk water in different parts of the tank, then it is a measurement error, perhaps due to algae on the probe itself photosynthesizing and using up CO2 when the sun hits it, causing it to report a false high pH. In any reef tank with any reasonable amount of flow, the pH inside of a single tank will be the same everywhere aside from areas with greatly restricted flow (such as deep in sand).

Try cleaning the probe in acid then recalibrate. :)