pH - is 7.2 too low?

[Inexplicable]

I am getting consistently low (7.2) pH in the morning for the past couple of months now. Throughout the day the pH raises to about 7.6, but never gets higher. To make sure my readings are correct, I borrowed a calibrated lab grade pH meter from one of my labs and it shows the same. SPS polyp extension is great and I am getting good growth rates. I only dose Seachem's Reef Builder and Advantage Calcium to maintain my SPS and my clam. I have two fish (clown and a damsel) and I don't overfeed. No recent deaths in the tank. I have a good skimmer, run a shallow sand bed with a remote DSB in my sump. I do a 15% water change every week with Reef Crystals salt, and pH of the new saltwater is ~8.3. I have a BRS ro/di unit with tds at 0 ppm. I run LEDs with a fan blowing across the surface of the water, so I'm not too concerned with CO2 degassing. I also took a cup of water outside and aerated it to see its effect, and only saw an increase in pH from 7.21 to 7.45, which still seems too low. I have read up as much as I can on pH and the consensus is to let it be what it wants to as long as everything else is in order. What I am curious about is this: is there any evidence of people who run a consistently low pH with success over time? And what could be causing my low pH? My reef is doing great with the exception of the low pH. I don’t want to cause undue stress to my inhabitants, however. Any advice is appreciated.

Here are my specs:
20 gallon mixed reef (mushrooms, zoas, leathers, LPS, heavy on SPS, 2 fish, 1 clam)
10 gallon sump/fuge with chaeto in reverse photo-period
specific gravity = 1.026 (with refractometer)
dKH = 9.0
Ca = 480 ppm
Mg = 1350
Phosphates, nitrates, nitrites, ammonia = undetectable
temperature = 81 F on controller, never wavers

[Percula9]

Measure a cup of water away from the tank.

[Inexplicable]

Originally Posted by Percula9

Measure a cup of water away from the tank.

Thanks but I did that already. If you read my post you would see it increased from 7.21 to 7.45 away from the tank.

[DoubleM 10]

what do you have for movement in the tank?

also are you tsting with the lights on or off?

[nanojg]

I know you used a calibrated lab grade ph probe, but I dont believe that your ph is 7.2 with a dkh of 9.

Either your dkh is wrong or your ph is wrong or you have a serious CO2 problem.

[Inexplicable]

For movement, I have two koralia nanos for 850 gph circulation and a Mag 5 return pump at 500 gph, so a total of over 60x turnover.

I was testing both with the main lights on and off. pH is lowest when the lights are off but even at the end of the day the pH is only at 7.6 or so.

I know the dKH seems wrong, but I checked with my Salifert test kit, and even dug out my old API alkalinity test kit and got similar results.

My main question was whether or not it is sustainable to keep the water at this pH.

[Percula9]

Try doing a chemical test and see what it is. I don't believe your pH is that low either. When was the pH probe last changed?

[Inexplicable]

Originally Posted by Percula9

Try doing a chemical test and see what it is. I don't believe your pH is that low either. When was the pH probe last changed?

OK, my lights just came on 30 minutes ago, and I just retested pH:
Salifert is approximately 7.4, definitely not 7.7
API is approximately 7.4 also (as low as it will go)
I also dug out some old litmus paper and it is about 7.3 in color

Just to see, I retested alkalinity with my API test kit and it is showing a dKH of 8.

[DustinB]

Is it cold in TN? Maybe high co2 levels? Have you tried opening some windows for an hour or 2 and seeing what happens? Maybe you have a leak in your heating system or you are lucky to have very good weather sealing on your house.

[Randy Holmes-Farley]

I too think the pH is not 7.2. Calibration fluids can be off, etc.

When you aerated the water with outside air, where did you do the pH measurement? outside? Or at the same location, where electrical interference might still be an issue?

If the pH is 7.2, it is a huge problem for animals with calcium carbonate skeletons since they will be slowly dissolving away.

[Inexplicable]

Originally Posted by Randy Holmes-Farley

When you aerated the water with outside air, where did you do the pH measurement? outside? Or at the same location, where electrical interference might still be an issue?

When I aerated the water outside I measured it outside. I started some aerating about 15 minutes ago and just tested it. The pH of that sample is 7.7 on the Salifert kit and 7.65 with my lab pH meter. Looks like I'm getting a little bit closer to where I should be. Should I consider dripping kalk? Or maybe injecting oxygen? I have a couple of SCUBA tanks but I'd rather not use them. Thanks for all the help guys.

[Percula9]

I think kalk would be a better idea. If CO2 is the problem, then a CO2 scrubber might be better in the long run.

[Inexplicable]

Originally Posted by DustinB

Is it cold in TN? Maybe high co2 levels? Have you tried opening some windows for an hour or 2 and seeing what happens? Maybe you have a leak in your heating system or you are lucky to have very good weather sealing on your house.

Interesting idea. I live in a heavily wooded area with tons of plants looming over my house. Could it be that the CO2 of the atmosphere surrounding my home is elevated at night time, and that could be causing the low pH? I've had the windows open off and on the past couple of days. My wife has a large planted aquarium in an adjacent room of the house. Should I consider putting this tank on reverse photo-period to see if that helps?

[Randy Holmes-Farley]

Try aerating the cup of water inside as well. That will tell you whether you just need more aeration, or whether you need fresher air to be used.

The trees are not pushing up your CO2 level (if anything, they lower it), but indoor cooking with gas, breathing, and any sort of unvented gas heater or fireplace will push up CO2 indoors.

Limewater is generally an excellent option for low pH.

This has more:

Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm

and

What Your Grandmother Never Told You About Lime
http://reefkeeping.com/issues/2005-01/rhf/index.htm

[borcu]

what will be the reading when aerated the water with outside air whatever ph reading?

[Inexplicable]

Aerating the water indoors leads to a maximum pH of about 7.5, no matter which test method I use. Thanks for the links to the articles Randy. I'll read through those again in more detail, but it seems that I can increase my alkalinity and then maintain it at a higher level with kalk. This should keep me at a higher, more constant pH.

[Randy Holmes-Farley]

Aerating the water indoors leads to a maximum pH of about 7.5, no matter which test method I use.

If you aerated long enough, then you have quite elevated indoor CO2, or the pH reading is off, or both. iIt should rise above 8.2 for seawater with 9 dKH alkalintiy and sufficient aeration with normal air.

[Randy Holmes-Farley]

what will be the reading when aerated the water with outside air whatever ph reading?


Perfectly aerated seawater will follow the blue line on this chart from my article above:



Figure 1. The relationship between alkalinity and pH for seawater equilibrated with air containing normal and elevated carbon dioxide levels. The green dot shows natural seawater equilibrated with normal air, and the curves reflect the result that would be obtained if the alkalinity were artificially raised or lowered.

[Inexplicable]

I agree with you that the pH should be higher than it is. However, I just now tested newly mixed saltwater here in my house and it is constant at a pH of 8.3. I also tested my wife's saltwater planted tank, which is at a pH of 8.3, and my FOWLR that is at 8.2. It is only my reef tank and the water within it that is low. Could there be another dissolved ion in the water causing a low pH besides CO2? Some sort of confounding factor only with my reef?

I left the cup inside aerating from earlier and just now tested it to be 7.5 after ~45 minutes. I opened all my windows this morning and even set up a box fan to blow in fresh air. We have all electric heating and appliances, no gas lines at all.

[nanojg]

Can you check your alk with another test kit?

[borcu]

Randy without you it is so boring

just a favour. we love rc. but we miss you.

[jdegrasse]

So putting all your posts together:
1) Your test kits are fine and the reading is correct.
2) CO2 is not the culprit, because the other tanks would be similarly affected. Plus you have a skimmer so that is aerating your tank.

So I have to think your water is contaminated with something that is driving down your pH.

[Inexplicable]

Originally Posted by nanojg

Can you check your alk with another test kit?

All I have is the API kit and the Salifert kit, neither expired. My LFS doesn't carry any others. I can order a different kit if you have a better one to suggest?

[Inexplicable]

Originally Posted by jdegrasse

So putting all your posts together:
1) Your test kits are fine and the reading is correct.
2) CO2 is not the culprit, because the other tanks would be similarly affected. Plus you have a skimmer so that is aerating your tank.

So I have to think your water is contaminated with something that is driving down your pH.

Yes, I think you have it correct. I would think, however, that my 15% weekly partial water changes would take care of the contamination.

Just to see, I think I'm going to do 20% water changes each day for the next several days. I already have salt mixed that I have tested to be fine. This should be slow enough to not shock the system too much. I don't want to cause a pH spike.

[Randy Holmes-Farley]

Could there be another dissolved ion in the water causing a low pH besides CO2? Some sort of confounding factor only with my reef?



If the carbonate alkalinity is correct, then no, there is no other way pH can be low except elevated CO2 in the water. Any other way of lowering pH must lower alkalinity.