11-23-2008, 02:56 PM
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I think there is a lot about the behavior of water ions that I (we) still don't understand. I also have problems with keeping ph down even though my gh and kh readings are relatively low (3 ish). If I leave my tap water in a bucket with a aerator for 24 hours it goes from 7.0 ph to almost 8. I have been attributing that to some type of trace metal that oxydizes or to the loss of carbin dioxide. I found that if I put my tap water in a sealed bell jar and pull a vacuum on it the ph does not change after 24 hours, so gas exchange is part of the process. In my tanks which are planted, ph is higher during the day when the plants are using the carbon dioxide but whether I use tap or RO water my ph always drifts to the very high 7s. This is regardless of substrate. However, if I use the same water in an unplanted tank with low light levels, the ph stabilizes at around 7.0. So, nothing correlates.
I don't completely understand these observations but I have seen similar behavior here.