Something in my QT tank is causing the pH to rise

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mcrousse

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HI all,

My well water pH out of the tap is 6.4. It is soft and acidic. I have an established 55 gallon tank that maintains this pH or goes to 6.5 between water changes. The problem is one of my quarantine tanks. There is something in there that is causing the pH to jump after water changes up from 6.4 to anywhere from 6.8 to 7.2 over approximately a 2 day span. There is no substrate in the tank. It only has: 1 fake rock, 1 jager heater, 1 fake plant, an aquaclear 20 with filter floss, pad, and Biomedia, and a thermometer. I cannot figure out what is going on! I would rather the pH stay about the same as my big tank so that when fish get moved over, they don't have to get drip acclimated, again. It would also make for easier water changes - not having to worry about pH shocking my fish.

Any ideas?
 
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mcrousse

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I thought it might be the fake rock, somehow, so I put it in a bucket overnight with fresh water from the tap. No change, still 6.4 the next day.
 
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mcrousse

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I changed out 80% of the water in the QT yesterday afternoon. I filled it up with water from the tap and tested it 2 hours later - 6.4. This morning it has shot up to 6.8. I am wondering how far it will go up.
 
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iRun

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dissolved CO2 depresses pH, which will then rise as the CO2 leaves the tank due to surface agitation from filter. That's one possibility
 
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mcrousse

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Thanks for your response. I did a series of experiments. I put out one container of tap water, and one container of the filter media - no airstones. After 3 days, all of them tested pH 6.8 (the ones with the filter media got there first), including the control container of plain tap water.
I put a gallon jug of tap water out, and put an airstone in it overnight, and it too went up to 6.8.
I think it was outgassing, but I was confused because my 55 gallon tank never gets up to 6.8. I do have a medium-size piece of malaysian driftwood in there (I was told it would not affect the pH but that must have been false), though, so perhaps that is keeping the pH down. In between water changes, it never exceeds 6.5 which is fine for the fish species I have in there. Now I have to re-acclimate any fish that is in my QT to the main tank, but fortunately the pH difference isn't huge.
 
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iRun

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Kudos to you for being so meticulous about your water quality! I'll be honest, I never test my water at all. I work for a utility as an analyst in a water quality lab so I've had my fill of water testing by the time I get home

I know that in the times I have tested my tanks, pH is lower than tap, and I've always assumed it's the wood.
 
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