pH Steady at 8.1... is this ok?

macphoto

macphoto

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Aug 19, 2005
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90g FOWLR, cycling, no residents yet. My pH has been holding steady at 8.1 for the past 5 days or so. From what I've read, a stable pH is much more important than the actual number, but the acceptable range I've read is 8.2 - 8.4. What steps (if any) should I take to raise the pH a bit?

I don't know if this is relevant or not, but I'll mention it... my tapwater has a very high pH (at least 8.4), but the water that comes out of my RO/DI reads 6.0 (the lower limit of my FW pH test kit). For some reason, I expected RO/DI water to be 7.0. Could this low pH of the RO/DI water be the reason why my SW is a bit low?

--Mike
 
Most people when they use RO water for top ups, mix it with kalkwasser to make limewater, and dripp it, it keeps you PH more stable and at a better LVL 8.3. But a Ph of 8.1 is nothing to be concerned about, when you do water changes, make sure the Ph is atleast 8.1.
 
pH 8.1 is fine. Most salt mixes are buffered to keep the pH about 8.2, so I do wonder why it is staying a little low in a new tank. The most likely explanations for your pH being low-ish are 1) acids generated during the cycle - which would show up as low alkalinity; 2) high CO2, possibly from the room air.

That opens 2 questions:
1) what is your alkalinity?
2) What happens to the pH of a sample of water if you aerate it vigorously in a well-ventilated room. If the pH goes up, the problem is dissolved CO2.

Your RO/DI water has a low pH because it is completely unbuffered (i.e., alkalinity near 0). That means the pH will drop when atmospheric CO2 dissolves in it. That is not a problem, because your seawater mix is buffered well, so the addition the addition of some weakly acidic water will not affect the pH.

In other words, don't worry about it too much, but it's worth keeping an eye on.
 
mogurnda said:
pH 8.1 is fine. Most salt mixes are buffered to keep the pH about 8.2, so I do wonder why it is staying a little low in a new tank.
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I confirmed the pH with a different test kit (Aquarium Pharm.)... this one has a color chip for 8.0 and 8.2, and the color I got was kind in between those two.

1) what is your alkalinity?
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Alk. is about 3.5 - 4.0.

2) What happens to the pH of a sample of water if you aerate it vigorously in a well-ventilated room. If the pH goes up, the problem is dissolved CO2.
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I will give this a shot.

--Mike
 
I side with mogurnda on the nitrification cycle. When cycling a system you will not have a stable pH.
 
Pineapple said:
I side with mogurnda on the nitrification cycle. When cycling a system you will not have a stable pH.
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Could be. When I said the alk was 3.5 - 4.0, I should have been more specific... before the cycle started, it was 4.0, now (cycle underway) it's 3.5.

--Mike
 
I still have not had a chance to do the aerated water pH test, but my tank pH is now 8.0, and the alk is 3.0.

One thing... I've been dosing the tank with Purple Up to help stimulate coralline growth. I've since read online that adding too much calcium can cause a drop in pH (or was it a drop in alkalinity?). However, I've been testing calcium at least once a day, and it's staying around 380 - 400, which doesn't seem too high.

--Mike
 
Ca is fine, but doesn't need to be any higher. I have not used purple up, but am leery of any product that adds Ca without some separate addition for alkalinity.

There may be a few things going on. The production of acids by your organisms may be neutralizing your buffers, and the consumption of carbonate by the coralline algae may be depleting alkalinity further.

Randy Holmes-Farley is one of my heroes. He writes clear articles about the chemistry issues we have to deal with. Here are a few you might look over when you get a little time:
low pH
calcium and alkalinity
 
mogurnda said:
Ca is fine, but doesn't need to be any higher. I have not used purple up, but am leery of any product that adds Ca without some separate addition for alkalinity.

There may be a few things going on. The production of acids by your organisms may be neutralizing your buffers, and the consumption of carbonate by the coralline algae may be depleting alkalinity further.

Randy Holmes-Farley is one of my heroes. He writes clear articles about the chemistry issues we have to deal with. Here are a few you might look over when you get a little time:
low pH
calcium and alkalinity
Click to expand...
Thank you for those links... very helpful.

I did the aerated sample test this evening, and it is identical to the water straight from the tank. So, I assume this rules out CO2 as the problem, and that it's probably related to the Purple Up dosing.

According to those articles, adding buffers is not a solution to pH problems by itself. But, since my alk is a bit low anyway, I went ahead and added some SeaChem Reef Buffer, which raised the pH back to 8.1, and the alk to 3.5. Was this a sound decision? I figure I'll add it as needed to maintain the alk at around 4.0 or 4.5.

--Mike
 
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