Reef Chemistry Question of the Day #171 Sodium Hydroxide Dosing

[redfishbluefish]

I generally would not, but Aquavitro has such a product (but don't believe all of their claims):

http://aquavitro.com/products/balance.html

Ah, for the pH chasers.....I wouldn't recommend this. Attempting to fix a problem by not addressing the root cause.....all too common today.

And Randy, you surprise me..........are you saying you don't believe all that Marketing hype? They wouldn't lie, would they?

 

[cvicente]

A.

 

[RudyB]

B.
It will raise both in the localized area until it is mixed with the remaining water. The later affects would depend on the amount that you used.

 

[SB Reef Lights]

@Randy Holmes-Farley

I think the other area this may be an issue is folks using the 275g IBC containers for water stations. I have 2 that where filled with Caustic Soda powder. Nasty stuff that burned like crazy when wet and felt super slimey. The issue for those folks might be, "How much do I impact the tank if the container is not 100% perfectly void of residual Sodium Hydroxide when I start making RODI or Salt Mix. Good news is it breaks down quickly in water, so with enough time and a strong hose, you can get pretty clean.

 

[Slm222]

B

 

[cowboy]

Ok so this question actually made my curiosity get the better of me so here are the results of 100ml aquarium water with 10MLS of sodium hydroxide .25 norm
Prior to adding sodium hydroxide
PH 8.41
Dkh 8.2

After
PH 9.11
Dkh 7.1
Sorry had a typo I used the .25 not the .602
So I'm going to have to go with C

 

[Randy Holmes-Farley]

Ok so this question actually made my curiosity get the better of me so here are the results of 100ml aquarium water with 10MLS of sodium hydroxide .25 norm
Prior to adding sodium hydroxide
PH 8.41
Dkh 8.2

After
PH 9.11
Dkh 7.1
Sorry had a typo I used the .25 not the .602
So I'm going to have to go with C

FWIW, an alk kit is measuring total alkalinity rather than carbonate alkalinity, so that is a complication of the question.

Did you really use 10 mL of 0.25 N? That should turn into a white mess of precipitate.

0.25 N hydroxide has a total alkalinity of 250 meq/L or 700 dKH. So at the concentration you added, the total alk would be around 76 dKH. Did you see a ton of magnesium hydroxide precipitate?

 

[SB Reef Lights]

I haven't put my Station online yet. Still at 14 TDS. Need more rinsing. However the pH test is odd. Guessing yellow is after blue on RSP kits? I don't have a more accurate test kit because I don't chase pH. But is like my make up water top be close.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley

I think the other area this may be an issue is folks using the 275g IBC containers for water stations. I have 2 that where filled with Caustic Soda powder. Nasty stuff that burned like crazy when wet and felt super slimey. The issue for those folks might be, "How much do I impact the tank if the container is not 100% perfectly void of residual Sodium Hydroxide when I start making RODI or Salt Mix. Good news is it breaks down quickly in water, so with enough time and a strong hose, you can get pretty clean.

It feels slimy because it is turning the oils (fats) in your skin into soap. That is not a preferred skin treatment.

 

[SB Reef Lights]

Really? I made a mud mask out of it. Rut-row.

 

[Rybren]

Is this a trick question? Does it matter if it is a he doing the dosing

 

[cowboy]

FWIW, an alk kit is measuring total alkalinity rather than carbonate alkalinity, so that is a complication of the question.

Did you really use 10 mL of 0.25 N? That should turn into a white mess of precipitate.

0.25 N hydroxide has a total alkalinity of 250 meq/L or 700 dKH. So at the concentration you added, the total alk would be around 76 dKH. Did you see a ton of magnesium hydroxide precipitate?

That it did and the color change was rather a bit different will double check thanks for the heads up on that. I was using a alk kit from api.

 

[Randy Holmes-Farley]

Is this a trick question? Does it matter if it is a he doing the dosing

Only if he is incompetent.

 

[cowboy]

Round two was way different on pH and total Dkh. Moral of the story never trust a petroleum engineer on chemistry we are horrible at it

 

[beaslbob]

I'm going with B. I don't currently understand a reason for alkalinity to not rise, and I know caustic soda has high pH. It is used in the oil industry (where I used to work), down hole, to increase the alkalinity and viscosity of the drilling mud. I'm not sure if there is a reason for alkalinity to initially drop like Jim speaks of.

no carbon. You need the carbon dioxide to react to increase the alk which is why my "b" was probably wrong and why Dr. Randy wanted the immediate effects before an gas action.

But then that just my wild guess.

 

[Randy Holmes-Farley]

And the answer...B. The pH rises and the carbonate alkalinity rises

Adding hydroxide itself raises total alkalinity since it is a contributor to total alkalinity, whether it does anything else or not.

But the question was carbonate alkalinity...

As soon as the hydroxide hits the water, there is conversion of bicarbonate into carbonate:

OH- + HCO3- --> H2O + CO3--

In a reef tank, not all of the added hydroxide ions do this. A very few combine with H+

H+ + OH- --> H2O

which is what raises the pH.

Some few added OH- also react with boric acid, silicic acid, ammonium, and the protonated forms of phosphate, to form the more basic forms of these chemicals. And some just stay in solution as OH-.

But the vast majority will be consumed by converting bicarbonate to carbonate.

So what effect does that have on carbonate alkalinity? Carbonate alkalinity (Ac) is:

Ac = [HCO3-} + 2[CO3--]

since carbonate counts twice and bicarbonate only once, any shift of bicarbonate into carbonate results in a rise in carbonate alkalinity, hence the answer to this question.

What happens after gas exchange (not this question)?

CO2 will enter the water, reducing the pH back toward where it started (but not quite all the way back since the alkalinity is higher) and the carbonate alkalinity will remain unchanged despite some conversion of carbonate to bicarbonate, because new bicarbonate is formed in the process:

CO2 + H2O --> H2CO3 (carbonic acid)

H2CO3 + CO3-- --> 2 HCO3-

This same process applies to all the other contributors to total alkalinity (such as borate), so total alkalinity is unchanged by adding CO2 (or removing CO2). This is called the Principle of Conservation of Alkalinity.

 

[Myka]

Woohoo!

 

[Randy Holmes-Farley]

Woohoo!

 

[beaslbob]

gee
Immediately after my post speculating b was wrong, Randy posts b is correct.

 

[Randy Holmes-Farley]

gee
Immediately after my post speculating b was wrong, Randy posts b is correct.

Better than if you were speculating after I posted it.