Does Low CO2 (And really High PH) reduce Kalk's ability to add ALK? (With fancy graphs)

[Wiskey]

Hello all!

I have a weird one, I've been dosing Kalk for a short time and when I'm home, with the dog and me breathing like mad all over the house it works fabulous, but when I leave for vacation I find that I need to tipple the ALK 2 part dosing to not even quite keep up. I know Kalk requires CO2 for the Alk part, is it possible that with no breathing it doesn't work as welll?

Here's the details:
My PH when I'm home on the left, I was gone on a work trip on the right, this probe was calibrated this month:

Normally I dose 80 ML of Core 7 Alk daily, when I'm gone I am pushing that to over 250 ML and the ALK still falls,.. Here is that graph:

At first I thought that my growth might be going through the roof when I travel, and it might, but my CA doesn't seem to be effected as dramatically, though it is a little bit. I did not change CA dosing at all:

What do you think? Could it be possible that I don't have the CO2 to make the ALK part of Kalk work when I'm gone? Or do you think the super high PH made my corals grow like crazy and I should run a skimmer airline outside to have that all the time?

Thank you!
Whiskey

 

[Randy Holmes-Farley]

No, there's never any concern that the hydroxide is not getting converted into bicarbonate and carbonate in a reef tank. A few leading hobby authors have misunderstood this fact, but it is easy to see that it is true.

pH is an exact measure of the concentration of hydroxide because H+ and OH- are exactly tied together. I can go into the exact reason and the math, but the table below shows the amounts of H+ and OH-, and the alkalinity that comes from that amount of OH- at any given pH.

As can be seen, at pH 9, the contribution of OH- to alkalinity is only 0.028 dKH, no matter how you got there. Thus, if the pH is below 9, the contribution of hydroxide to alkalinity is always less than 0.028/7 = 0.4% of the total alk.

pH	[H+]	[OH-]	Alk (meq/L)	Alk (dKH)
0	1	1E-14	1E-11	2.8E-11​
1	0.1	1E-13	1E-10	2.8E-10​
2	0.01	1E-12	0.000000001	2.8E-09​
3	0.001	1E-11	0.00000001	2.8E-08​
4	0.0001	1E-10	0.0000001	0.00000028​
5	0.00001	0.000000001	0.000001	0.0000028​
6	0.000001	0.00000001	0.00001	0.000028​
7	0.0000001	0.0000001	0.0001	0.00028​
8	0.00000001	0.000001	0.001	0.0028​
9	0.000000001	0.00001	0.01	0.028​
10	1E-10	0.0001	0.1	0.28​
11	1E-11	0.001	1	2.8​
12	1E-12	0.01	10	28​
13	1E-13	0.1	100	280​
14	1E-14	1	1000	2800​

 

[Randy Holmes-Farley]

The likely explanation for your observation is that demand for alk and calcium rises fast as pH rises (when you aren't home), both because corals grow faster and abiotic precipitation of calcium carbonate increases.

When there is balanced over or underdosing relative to demand, that always shows up first in changes in alk because there is a much larger reservoir of calcium than alk in seawater, making the change in calcium a smaller percentage of the total calcium than the balanced change in alk as a percentage of the total alk present.

 

[Wiskey]

Okay, so that brings up another possibility. We know that the Kalk is still working, and even at PH of 9 it would still have plenty of CO2 to produce the ALK that is required.

So! The high consumption must be either precipitation, or growth. I'm not seeing precipitation all over the place, so I'm leaning toward growth.

Is a PH of 8.68 safe? Should I pull air from outside into my skimmer to get my daily PH closer to that number? It wouldn't be hard to do, in fact I used to have it that way and stopped pulling from outside when I added Kalk to bring my PH down.

Thank you once again for all the help!!!!
Whiskey

 

[Randy Holmes-Farley]

Okay, so that brings up another possibility. We know that the Kalk is still working, and even at PH of 9 it would still have plenty of CO2 to produce the ALK that is required.

So! The high consumption must be either precipitation, or growth. I'm not seeing precipitation all over the place, so I'm leaning toward growth.

Is a PH of 8.68 safe? Should I pull air from outside into my skimmer to get my daily PH closer to that number? It wouldn't be hard to do, in fact I used to have it that way and stopped pulling from outside when I added Kalk to bring my PH down.

Thank you once again for all the help!!!!
Whiskey

You do not always visibly see it without looking carefully. It's a risk at the pH you are at. Sand hardening, pump impeller coatings, etc.

That pH (8.68) seems experimentally high to me, but it also may not be accurate. It's very rare to see pH that high.

 

[Wiskey]

I thought there might be a measurement error as well, that's why I calibrated the probe when I started dosing Kalk. It could be off, but I suspect it's not too far off.

When my dog is home it bounces between 8.15 and 8.45 which isn't too bad, but when the house is totally empty for a few days it really climbs. Right now I'm dosing 4000ML (just over 1 Gallon) per day of saturated Limewater along with 200 ML per day of Triton Core 7 which also has a PH raising effect to a 135G SPS tank with a 50G sump, and 40G SPS Frag tank.

Maybe I should actually back off the Kalk when I travel just to keep the PH a little bit lower? I don't want to rely on a statement in the APEX to kill the Kalk at a certain PH because that would be unpredictable, though I wouldn't mind that as a backup.

What do you think the upper limit should be? I've always been concerned with the lower limit in the past, I don't think I've had a reason to wonder about the upper limit.

Whiskey

 

[Randy Holmes-Farley]

The higher you go the more likely precipitation and pump problems are. I’d consider bring it down with more aeration.

 

[Wiskey]

The higher you go the more likely precipitation and pump problems are. I’d consider bring it down with more aeration.

Makes sense. Thank you Randy! I'll back the Kalk off when I'm going to have the dog in boarding, and preemptively raise the 2 part numbers. After a couple work trips I'll have a pretty good idea of where I need to be with that.

Thank you,
Whiskey

 

[Wiskey]

I brought down the daily Kalk dosing toward the end of the photo period, and reduced overall dosing by 700 ML/Day so my total is now 3300 ML instead of 4000.

I'm hoping to keep PH under 8.4 during the day, but keep it high at night. I set the Kalk pump so that if PH goes above 8.5 it will shut down.

Tank you,
Whiskey