Some results from sodium hydroxide dosing

[Gigajoulz]

There's no issue with dosing hydroxide and lack of carbonate/bicarbonate unless you drive the pH too high (higher than you'd go).

This is a cut and paste from my limewater/kalkwasser article which has the same "concern":


...and the hydroxide ions supply alkalinity. Hydroxide itself provides alkalinity (both by definition and as measured with an alkalinity test), but corals consume alkalinity as bicarbonate, not hydroxide. Fortunately, when hydroxide is used in a reef aquarium, it quickly combines with atmospheric and dissolved carbon dioxide and bicarbonate to form bicarbonate and carbonate:

4. OH- + CO2 ---> HCO3-

5. OH- + HCO3- ---> CO3-- + H2O

In an aquarium with an acceptable pH, there is no concern that the alkalinity provided by hydroxide is any different from any other carbonate alkalinity supplement. The hydroxide immediately disappears into the bicarbonate/carbonate system. In other words, the amount of hydroxide present in aquarium water is really a function of only pH (regardless of what has been added), and at any pH below 9, it is an insignificant factor in alkalinity tests (much less than 0.1 meq/L). Consequently, the fact that alkalinity is initially supplied as hydroxide is not to be viewed as problematic, except as it impacts pH.

I think this is what I have been missing, what is the HO- doing that adds alkalinity if "alkalinity" is some form of carbonate... I found the question poised much better than I've attempted. The whole time I've mistaken the Hydrogen in carbonic acid as coming from another source when its really just the water from the tank dissolving the CO2; like H2(CO2)O -> which then falls apart into (H+) + HCO3- at a given pH, and THAT (H+) is whats tied up with the HO-.... add another HO- and the HCO3- -> CO3 + H2O at a higher pH.

did I mention I was BAD at stoichiometry?

Its also the equilibrium with the atmosphere I'm still a little fuzzy on, specifically how this contributes to the carbonate system in general. What's confusing me there is I've read (misread?) about hydroxide dosing allowing for the uptake of CO2, but I guess that makes sense now because the tank it out of equilibrium, but the concentration is already "determined" by the pH and what was dosed. does that all sorta add up better?

 

[sean151]

For the CO2; An extreme example would be tank and air are at 500ppm. You add calcium hydroxide (or any other hydroxide) which drops your tank CO2 down to 450, thus raising Ph. As your skimmer works to equalize the CO2 to the air value the Ph drops back down. The Alk effect stays, but the CO2 drop is temporary. This is the same reason that your Ph will fluctuate during the day and night cycle, CO2 rising and falling, but potentially no change to Alk.

 

[Randy Holmes-Farley]

I think this is what I have been missing, what is the HO- doing that adds alkalinity if "alkalinity" is some form of carbonate... I found the question poised much better than I've attempted. The whole time I've mistaken the Hydrogen in carbonic acid as coming from another source when its really just the water from the tank dissolving the CO2; like H2(CO2)O -> which then falls apart into (H+) + HCO3- at a given pH, and THAT (H+) is whats tied up with the HO-.... add another HO- and the HCO3- -> CO3 + H2O at a higher pH.

did I mention I was BAD at stoichiometry?

Its also the equilibrium with the atmosphere I'm still a little fuzzy on, specifically how this contributes to the carbonate system in general. What's confusing me there is I've read (misread?) about hydroxide dosing allowing for the uptake of CO2, but I guess that makes sense now because the tank it out of equilibrium, but the concentration is already "determined" by the pH and what was dosed. does that all sorta add up better?

Total alkalinity (as measured by any normal kits we use) is not just a form of carbonate. It is anything that takes up an H+ as the pH is dropped to about 4.3. Here's the full equation (TA = total alkalinity), showing that there are lots more contributors, including hydroxide. Sodium hydroxide solution has alk that can be measured with an ordinary alk titration test. Other than that, what you write is correct about what happens to hydroxide after adding it, although there are lots of other things that happen too. The article below has a lot more.

TA = [HCO3–] + 2[CO3—] + [B(OH)4–] + [OH–] + [Si(OH)3O–] + [MgOH+] + [HPO4—] + 2[PO4—] – [H+]

Chemistry and the Aquarium: What is Alkalinity?

Randy provides an overview of alkalinity as to why it's important, how it's measured, and how can it be tested.

reefs.com

 

[Scott Max]

Hello everyone, new to the forum.
Thinking about using sodium hydroxide to raise my pH, which hovers between 7.6-7.8 (Perhaps I should leave well enough alone). At 283 grams per gallon concentration, what would be a good daily dosing amount to start with? My tank is a 20 gallon mixed reef, 8 months old. Parameters are (using Hanna testers):

CA	514​
MG	1250​
Alk	9​
pH	7.7​
Phos	0.058​
Nitrate	2.4​
Ammonia	0.0​
Salinity	1.025​
Temperature	78​

15lbs live rock with live sand, Protein skimmer, HOB filter, two power heads, 3 fish, 8 LPS, one clam (all doing well). Tropic Marin Pro Reef salt. Poor air circulation in the home. Thank you.

 

[Randy Holmes-Farley]

Hello everyone, new to the forum.
Thinking about using sodium hydroxide to raise my pH, which hovers between 7.6-7.8 (Perhaps I should leave well enough alone). At 283 grams per gallon concentration, what would be a good daily dosing amount to start with? My tank is a 20 gallon mixed reef, 8 months old. Parameters are (using Hanna testers):

CA	514​
MG	1250​
Alk	9​
pH	7.7​
Phos	0.058​
Nitrate	2.4​
Ammonia	0.0​
Salinity	1.025​
Temperature	78​

15lbs live rock with live sand, Protein skimmer, HOB filter, two power heads, 3 fish, 8 LPS, one clam (all doing well). Tropic Marin Pro Reef salt. Poor air circulation in the home. Thank you.

I’d start by dosing it based on your known alk demand (if you know). Do you know it?

If you are dosing nothing and alk is still 9 dKH, I don’t recommend dosing any and I’d look for a different way to raise pH unless you know that you want alk higher than 9 dKH.

 

[Miami Reef]

How do you know the 7.7 pH reading is accurate? I doubt it if the alk is around 9dKH.

What are you using to test pH? If it’s a standard test kit (using drops or powder) they are not accurate. If it’s a double junction 2 point calibration probe (like what Apex uses) recalibrate it with the Apex, Milwaukee, or Hanna standards.

 

[Scott Max]

Thanks for your reply. I will hold off and test my alk consumption over the course of several weeks and calibrate my Hanna meter using known Hanna pH standards. Thanks again!

 

[Scott Max]

I’d start by dosing it based on your known alk demand (if you know). Do you know it?

If you are dosing nothing and alk is still 9 dKH, I don’t recommend dosing any and I’d look for a different way to raise pH unless you know that you want alk higher than 9 dKH.

Hi Randy. So I have determined that my 20 gallon nano is utilizing less than 0.25 dKH per day. What is a good daily dosing starting point of sodium hydroxide?

 

[Scott Max]

Hi Randy. So I have determined that my 20 gallon nano is utilizing less than 0.25 dKH per day. What is a good daily dosing starting point of sodium hydroxide?

My alkalinity runs about 8 on average, pH stable at 7.8, shooting for 8.2 pH for coral growth. All other water parameters within normal range. I have decent aeration, HOB filter, HOB skimmer, and two powerheads pointing slightly towards the surface, 15 lbs live rock. I am at a loss with regards to daily dosing amount. (283g NAOH per gallon RODI water.). Thanks

 

[Randy Holmes-Farley]

Hi Randy. So I have determined that my 20 gallon nano is utilizing less than 0.25 dKH per day. What is a good daily dosing starting point of sodium hydroxide?

Use this calculator and Randy’s recipe 1 to deliver 0.25 dKH.

Reef Chemistry Calculator

reef.diesyst.com

 

[saintdrm]

Hi Randy,
I would like to dose Sodium Hydroxide to raise my pH, it is 7.6 at night and 7.9 in the day, my tank is 100g , I currently use all for reef and my alk is at 8.5 and dose around 25ml per day to keep that alk stable. I use all for reef because its convenient (takes care of all trace elements etc.) and allows me to run a no water change reef. I see a lot of people use the Kalk method but using that would add too much calcium in conjunction with the AFR and throw off all the other elements ratios and the dosage volume is an issue for me. Is there an option to use the sodium hydroxide for pH control and still be able to use the AFR and just dose those two?

My thinking is to dose the sodium hydroxide at a rate to keep pH stable, dose AFR at a rate to keep calcium stable ( which is the recommended way to dose AFR anyways), ALK will fluctuate but according to the Chris Meckley method, that doesn't matter too much as long as the pH is stable. The problem I see is the rising sodium, how much of an issue is that and how would I go about countering it? Is my entire plan garbage lol?

 

[Randy Holmes-Farley]

Sorry, that won’t work out. Sodium hydroxide is just a high pH alk supplement and you’d be double dosing on alk.

If you want to go this route, use the sodium hydroxide diy two part with Balling Part C and Tropic Marin A and K for trace elements.

 

[saintdrm]

Thank you , I had not considered that approach, that's actually perfect.

 

[saintdrm]

Randy , Could I use Tropic Marin A and K and Bio magnesium (basically all for reef without the carbo calcium) then use you sodium hydroxide DIY 2part without the 261.2 g of magnesium chloride hexahydrate? , Balling Part C is out of stock at BRS atm.

 

[Miami Reef]

Please recalibrate your pH probe. It’s very difficult to achieve 7.6 pH. I think your pH might be higher than you think.

What type of pH rest do you use?

 

[saintdrm]

Yes, I am not only going to calibrate it I am installing a new probe today, I use an apex pH probe . but those values I listed are accurate, don't underestimate my skills at being bad....lol, tested with 3 different tests one of which is a professional water quality lab, apex and Hanna colorimeter. I live in an apartment with no outside ventilation (no windows that open etc.) and very high CO2 levels, I also use CO2 scrubbing media on my skimmer. I took a vacation for two weeks and no one was in the hose and the pH rose to above 8.2 , best two weeks for the tank ever.