Bloody PH - The Planted Tank Forum
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post #1 of 4 (permalink) Old 07-26-2012, 05:22 PM Thread Starter
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Bloody PH

When I first filled the tank the Ph was the same as my tap water approx 7.4, since re-scaping and re filling it now reads approx 8.4!

I can only put it down to one of two things, I smashed one of the rocks which may be causing it but I also added another rock that was not in it the first time which is the same as the others.

The tap water is still the same so it can only be one of those two things, now my question is if I do not take them out and the Ph stays about 8.4ish will using Co2 counter the affects if it is the rock buffering the water and will it be able to bring the Ph down to a constant and stable level of say 7 - 7.4?

One other cause that has crossed my mind but I feel is unlikely is evaporation, the last couple of days it has been close to 90 in the room and the sump water level has gone down by about 15L in an approx 600L system over about 36hrs, would that be enough to dilute and concentrate the minerals in the tap water enough to affect the PH so much?

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post #2 of 4 (permalink) Old 07-26-2012, 08:03 PM
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Get your hands on some hydrochloric acid and test the rock you find suspicious. Limestone will bubble if you drop HCl on it. That could potentially raise your tank PH. I kind of think it won't raise it much, since I have a big chunk of limestone in my HOB filter and the pH doesn't go much over 6.5. My water is very soft, and I was trying to give the pH some stability.

Some substrates such as eco-complete can raise the Ph of the tank in the short term. I don't know if eco-complete still has this problem, but the effect is short lived, so I wouldn't worry much about it.

In any case, let the pH do what it's going to do. If the pH of your tap water is still 7.4, then just do a big water change before adding fish. You can also try adding driftwood, or filtering through organic peat moss. Take it easy on the changes if you have fish in it now.

Truth be told, fish can withstand out of range pH values a lot better than they can withstand their owner trying to mess with the pH all the time.
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post #3 of 4 (permalink) Old 07-26-2012, 09:50 PM
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how fast rock like limestone will raise the pH of your tank depends on your water's buffering capacity (KH)- if it has very little then rock can raise your pH exponentially and very quickly, if it has a lot then rock might not raise your pH at all.
CO2, especially pressurized, can lower your pH- yes, but the hardness of the water will remain the same. so if your pH goes down to 7.4 from your current 8.4, the raised GH/TDS will remain the same, it's more or less an illusion. the only way to truly soften water is to filter out the minerals.
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post #4 of 4 (permalink) Old 07-26-2012, 11:02 PM
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When you let limestone dissolve in the water, raising the KH, the pH goes up. Add CO2 to drop the pH and the limestone will just dissolve faster, raising the KH even more, and the pH will go back up. With limestone in the tank you need to do big water changes often. If you change 50% of the water once a week, you limit the maximum KH, and by doing that, you limit the maximum pH. Assume the limestone raises the KH by 2 degrees a week. Doing 50% water changes weekly should limit the maximum KH increase to 4 degrees.

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