Confusing PH levels help

CJLand

All tests were conducted with API master test kit and API GH/KH test kit. I tested my tap water earlier to find out the PH was about 7.5 (highest end of low PH test, lowest end of high PH test). I tested my 54 gallon tank to find the PH was 8.2. I know that the PH straight out of the tap isn’t the true PH because of the dissolved co2. And once the water outgasses, then the true PH is shown. I also tested my 20 gallon high. Also 8.2 ph. The 54 has been up and running aroun 6 months, the 20 high has been like 8 or 9 years. I tested one of my 20g long quarantine tanks which is just about finished cycling and has been up for a month. The PH is 7.5 like the tap. I haven’t added water to any of the tanks in weeks, so none of the gasses should be there causing the false ph. All 3 of the mentioned tanks have pretty good aeration and flow. Aeration releases co2 from the water, which would result in a higher ph as well right? But why is the newer 20 gallon long have the same ph as the tap if no tap water has been added in weeks? Wouldn’t the true ph be showing, especially with the addition of the surface agitation? I tested another one of my tanks which has been up for years and it also has an 8.2 ph, but has poor flow and aeration. Any ideas or explanations? Also, kinda unrelated to the PH confusion, but my water is pretty soft for having a high ph like 8.2. Out of the tap dGH is 5 and dKH is 4. Any particular reason for something like that? Thanks for any explanation!
 

CrackerboxPalace

The lower pH could be caused by leaf litter, driftwood, certain substrates etc. One thing to consider is that in a heavily stocked tank, the fish respire more CO2. Probably not enough to noticeably change it, but could still be a factor if one tank is dramatically more stocked than another tank.

pH also goes down with higher temperatures.
 

CJLand

The lower pH could be caused by leaf litter, driftwood, certain substrates etc. One thing to consider is that in a heavily stocked tank, the fish respire more CO2. Probably not enough to noticeably change it, but could still be a factor if one tank is dramatically more stocked than another tank.

pH also goes down with higher temperatures.
None of the tanks have any kind of leaf litter, and all the substrate is inert normal gravel. In the 54 I have some manzanita wood but the ph is still 8.2. And none of them are very stocked at all at the moment. The thing that does make sense is the temperature thing. The quarantine is the only one with a ph of 7.5 but I do have it set to 83F as it cycles since bacteria grows a bit better when warmer. Maybe that’s why it’s lower. Thanks for the help!
 

CrackerboxPalace

I don't believe the temperature could cause such a drastic change in pH. The difference in tank temps is too small for that to be the only factor.

Any seriyu stone in the tank with a higher pH? very confusing.
 

mattgirl

One explanation might be that over time minerals (things we don't normally test for) have built up in the tanks that have been running longer. Since the others have been running for quite a while, unless you charted the pH as they were cycling, you can't know if the pH in them was the same as the new tank is now. Over time the pH in this tank may end up matching the other tanks.
 

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