Question about pH boost vs different volumes to maintain the same alkalinity

[Miami Reef]

Let’s assume we have a 100gal tank.

In the first scenario, we need 200mL of a sodium hydroxide solution to maintain 8dKH

In the second scenario, we need 400mL of the same sodium hydroxide solution to maintain 8dKH.


Is the pH boost of both scenarios the same, or is it different?

 

[Salty_Northerner]

This a question or a quiz?

 

[Miami Reef]

This a question or a quiz?

It’s was initially a question, although I wouldn’t mind if we made it into a quiz where @Randy Holmes-Farley would give us the final answer by the end.

 

[Salty_Northerner]

Id think the pH would change?

 

[Reefering1]

I would expect there ph in the higher demand tank to be higher. For 2 reasons- double the sodium hydroxide added and double the consumption (growth increases ph also)

 

[Court_Appointed_Hypeman]

It will further increase PH.

 

[Randy Holmes-Farley Verified Community Expert]

The pH change is determined by the amount of hydroxide added, and is not appreciably impacted by how much water it is dissolved in for dosing.

Thus, 1 g in 100 mL ro/di has the same boost as 1 g in 1,000 mL, while 2 g will have twice the effect when in either 100 mL or 1,000 mL.

 

[Miami Reef]

The pH change is determined by the amount of hydroxide added, and is not appreciably impacted by how much water it is dissolved in for dosing.

Thus, 1 g in 100 mL ro/di has the same boost as 1 g in 1,000 mL, while 2 g will have twice the effect when in either 100 mL or 1,000 mL.

I don’t think I made my question clear.

If organisms are releasing H+ back after consume bicarbonate/carbonate, then will the pH will go back to the way it was?

Thus, if I have a crazy stocked tank that consumes a massive amount of hydroxide, vs a minimally stocked tank that doesn‘t, but both tanks are maintained at 8dKH, will it be the same effect in pH boost?


I basically want to know if the pH reverts back when organisms pump the H+ back out.

Is the pH boost from hydroxide logarithmic: the larger the demand is, the higher the pH boost will be?

 

[Randy Holmes-Farley Verified Community Expert]

Organisms deposited calcium carbonate,

If you dose carbonate, there’s a pH boost when adding it and a pH decrease when it is consumed. There is no net overall effect. This one may surprise folks.

If you dose bicarbonate, there’s a pH drop when adding it and a pH decrease when carbonate is consumed. The net effect is a pH drop.

If you dose hydroxide, there’s a pH boost when adding it and a pH decrease when carbonate is consumed. The net effect is a pH boost.

The higher the alk demand, the more of each of these you need to add, and the more intense is the net overall effect of each.

 

[Randy Holmes-Farley Verified Community Expert]

Thus, if I have a crazy stocked tank that consumes a massive amount of hydroxide, vs a minimally stocked tank that doesn‘t, but both tanks are maintained at 8dKH, will it be the same effect in pH boost?

Specifically on that question, The more hydroxide you add to maintain the same alk, the higher the overall pH effect.

 

[Miami Reef]

Organisms deposited calcium carbonate,

If you dose carbonate, there’s a pH boost when adding it and a pH decrease when it is consumed. There is no net overall effect. This one may surprise folks.

If you dose bicarbonate, there’s a pH drop when adding it and a pH decrease when carbonate is consumed. The net effect is a pH drop.

If you dose hydroxide, there’s a pH boost when adding it and a pH decrease when carbonate is consumed. The net effect is a pH boost.

The higher the alk demand, the more of each of these you need to add, and the more intense is the net overall effect of each.

Wow. I didn’t know this! Thank you so much.