Protein Skimmers & KH/Alkalinity

[acropora1981]

Has anyone ever heard of protein skimming reducing KH or alkalinity? I just had a heated debate with a fellow who is absolutely convinced that protein skimming reduces alkalinity, but I've not heard of this in my 15 yrs of reef keeping.

 

[Randy Holmes-Farley]

No, skimmers cannot reduce alkalinity.

They may remove other things that could allows corals and coralline algae to calcify faster, thereby reducing alkalinity, so that could be a basis for his statement, even if not accurate.

 

[acropora1981]

No, skimmers cannot reduce alkalinity.

They may remove other things that could allows corals and coralline algae to calcify faster, thereby reducing alkalinity, so that could be a basis for his statement, even if not accurate.

Thanks Randy. My response to him was that in my 15 years I had not read anything of the sort, that I couldn't see how it could happen that way, and that yes, its entirely possible for your KH to go from 10 to 8 in 3 days if you have a good amount of corals. He wouldn't budge. "You fellas all looove yer protein skimmers. Those damn things make my KH crash out and bring down the ph!"

Then I went into how skimmer raise pH via off gassing of CO2, but he wasnt interested in that.... TY for confirmation.

 

[bobbychullo]

i've read they will remove calcium from the water but not KH/Alk. you can do a search on the internet, someone tested it. iirc, depending on how wet you skim, it pulled out a good amount of calcium.

 

[Randy Holmes-Farley]

Skimmers don't remove soluble calcium appreciably more than is already present in the tank water that the skimmate contains (which, of course, contains 300-600 ppm calcium), but skimmers can remove calcium carbonate particulates (like stirred up fine sand, tiny suspended creatures with calcium carbonate skeletons, etc.).

 

[rkaires]

Hey Randy,

What is you take on needle wheel skimmers removing or depleting K+ form the water. I've often seen this debated on other forums.

Thanks,

 

[Randy Holmes-Farley]

Potassium itself in the water cannot be skimmed out with any type of skimmer.

Whole bacteria can be skimmed out with all of whatever is inside of them, including potassium. Many bacteria tend to have higher internal than external potassium concentrations. So skimmed bacteria could take out some potassium relative to sodium.

Experimentally, Ron Shimek did not find potassium to be elevated in skimmate relative to seawater, and the skimmer sludge was only slightly elevated in potassium:

http://reefkeeping.com/issues/2002-12/rs/feature/index.php

 

[rkaires]

Thank you,

 

[Randy Holmes-Farley]

Sure thing.

I would add one additional point.

Folks should not assume that organic carbon dosing necessarily results in depletion of potassium by this route. That is because foods that come into the tank also have potassium elevated relative to tank water because they are made of cells that sequester potassium inside of them just as bacteria (or macroalgae) used for export may remove potassium. In fact, foods may have a higher potassium to sodium ratio than does skimmate or skimmer sludge based on tests like Ron Shimek’s food and skimmate studies.

http://replay.waybackmachine.org/20010303131908/http://www.animalnetwork.com/fish/data/foods.asp

So overall, one might get a balance, and that seems what a number of studies have shown. Ron's data on tanks, for example, or my own data for my tank with heavy organic carbon dosing and no apparent depletion of potassium.

The one thing that is a potential potassium depleter is zeolite use by zeovit users. The zeolite itself may bind potassium from the water, in addition to any export by bacteria (on the media, by skimming, etc).

 

[bobbychullo]

thanks for clearing that up

 

[Randy Holmes-Farley]

:thumbsup:

Happy Reefing.

 

[rkaires]

Sure thing.

I would add one additional point.

Folks should not assume that organic carbon dosing necessarily results in depletion of potassium by this route. That is because foods that come into the tank also have potassium elevated relative to tank water because they are made of cells that sequester potassium inside of them just as bacteria (or macroalgae) used for export may remove potassium. In fact, foods may have a higher potassium to sodium ratio than does skimmate or skimmer sludge based on tests like Ron Shimek's food and skimmate studies.

http://replay.waybackmachine.org/20010303131908/http://www.animalnetwork.com/fish/data/foods.asp

So overall, one might get a balance, and that seems what a number of studies have shown. Ron's data on tanks, for example, or my own data for my tank with heavy organic carbon dosing and no apparent depletion of potassium.

The one thing that is a potential potassium depleter is zeolite use by zeovit users. The zeolite itself may bind potassium from the water, in addition to any export by bacteria (on the media, by skimming, etc).

Great info Randy!

Thanks,

 

[mattliu]

If protein skimming accelerates gas exchange, why wouldn't it accelerate the depletion of alkalinity ?

http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic Acid.html

 

[Dan_P]

If protein skimming accelerates gas exchange, why wouldn't it accelerate the depletion of alkalinity ?

http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic Acid.html

Firstly, gas exchange equilibrates the CO2 level in the water with the air that surrounds the aquarium. So, you can take just so much out. Secondly, lowering the CO2 level in the aquarium shifts the amount of HCO3- to more CO3-- which raises the pH. The alkalinity stays the same, i.e., the sum of the negative charges is constant. H+ will reduce alkalinity.

 

[mattliu]

I was thinking the opposite. As carbonic acid is formed from dissolved CO2, more CO2 from the atmosphere fills the void to maintain equilibrium. The link verifies the chemistry. The argument really centers around whether a skimmer effects the rate of gas exchange.

 

[Dan_P]

I was thinking the opposite. As carbonic acid is formed from dissolved CO2, more CO2 from the atmosphere fills the void to maintain equilibrium. The link verifies the chemistry. The argument really centers around whether a skimmer effects the rate of gas exchange.

Not quite right. There are no voids to be filled. The equilibrium is soley driven by free energy. Adding CO2 and thus increasing the concentration of carbonic acid only shifts the equilibrium towards more HCO3-, but never less alkalinity. That stays the same.

Skimmers do improve gas exchange. Any stream of air, i.e., any increase in surface area of gas/water interface, will improve gas exchange.

There really isn't an arguement here as much as a misunderstanding of thermodynamics.

 

[mattliu]

Atmospheric water is acidic. Alkalinity represents a gradient. Second law of thermodynamics will return it to its acidic state. Protein skimming accelerates the process.

 

[mattliu]

I read Randy's article on alkalinity. I was defining alkalinity differently. Based on two definitions, a substance can become less alkaline(lower pH) but have its alkalinity remain the same.

 

[ReefTeacher]

mattliu,
the 2nd law of thermos is a statement about entropy of the universe, it does not claim that water had any sort of memory regarding its former pH. Rain water is indeed acidic due to emissions in the atmosphere, but water does not return to any particular state, it simply reaches equilibrium with the atmosphere in your house. If you have a very air-tight home, CO2 levels could be elevated, but skimming has no effect on the equilibrium. (although it could affect the kinetics).