Why activated carbon can leach phosphate ?

[Charles Silva]

Hello reefers

Why some activated carbon brands clains that is phosphate free ?

How is the manufacturing process to have or not phosphate in the composition or is it related to the raw material ?

In terms of price there is a big difference from freshwater activated carbon and marine and Im trying to understand the reason or if we must always use the most expensive.

Thanks
Charles Silva
Rio de Janeiro - Brazil

 

[Randy Holmes-Farley Verified Community Expert]

Ignore such claims and use a quality carbon without concern. Folks misunderstand tests where they put some carbon in a small amount of water and detect phosphate in the water. But it is likely very little phosphate that makes the small volume reach a high level. Foods are always a bigger source.

ROX 0.8 is a good choice, as are others.

 

[norakat]

There are so many articles saying activated carbon leeches phosphates into the water. We want to know why?

 

[Randy Holmes-Farley Verified Community Expert]

There are so many articles saying activated carbon leeches phosphates into the water. We want to know why?

The amount is typically too small to be important, and I address that part below. But the why is easy: there is phosphorus in the materials (such as wood) used to make activated carbon, and if it is not washed away by the manufacturer, some may remain loosely associated with the surface and can be released.

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both

Foods are by far the most important source of phosphate in most aquariums. In considering whether sources of phosphate other than foods are important, one must carefully look to the actual amounts involved to determine whether other sources are even worth trying to minimize.

reefs.com

From it:


The same sort of calculation applies to analyzing other phosphate issues, such as the GAC in scenario three. The issue of finding “high” phosphate in GAC soaked in fresh water was frequently quoted as a reason to use one or the other brand of GAC, and probably still is. But simple analysis as shown above for the food rinsing puts the lie to this being a big problem.

One needs to consider how much GAC one will really use in the aquarium and how often it is added in order to interpret how important the added phosphate is. A typical recommendation might be 1 cup of GAC per 100 gallons of aquarium water, and to change it in 4-6 weeks. Let’s assume we detect 0.5 ppm phosphate when a teaspoon is placed in a cup of water, and we get scared by the dark blue color during the test. Is this reasonable? That 0.5 ppm from a teaspoon in a cup of water translates to 0.015 ppm phosphate when a cup is used in 100 gallons.

That 0.015 ppm may be significant, being a typical target concentration level for reef aquaria and amounting to about half to a twentieth of the amount added daily in foods, but remember, it is used for 4-6 weeks. During those 4-6 weeks before the next replacement, foods add 50-700 times as much phosphate. So while it is not unreasonable to look for another brand of GAC, to blame phosphate or algae issues in the aquarium on its use would stretch credibility because it is a very tiny portion of the total phosphate being added.

 

[norakat]

According to this article (Activated carbon comparison) 3 of the brands out of 8, tested as high as 1 PPM while the others were lower by a factor of 4 or more.

Not sure how to translate that to a real world scenario but the article seems to make the findings significant.

I became interested after I noticed I had algae problems increase significantly after a filter change w more carbon then usual. The amount of food I fed was the same.

 

[EricR]

According to this article (Activated carbon comparison) 3 of the brands out of 8, tested as high as 1 PPM while the others were lower by a factor of 4 or more.

Not sure how to translate that to a real world scenario but the article seems to make the findings significant.

I became interested after I noticed I had algae problems increase significantly after a filter change w more carbon then usual. The amount of food I fed was the same.

Test you linked was conducted in just 250 mL of water.
I think, to Randy's point, even 1 ppm of Phosphate in 250 mL of water translates into insignificant amounts in aquariums (which contain GALLONS of water).

EDIT -- quick calculation sample using 75 liters (20 gallons) tank with worst case of 1 ppm from that test you linked:

1 ppm in 250 mL translates into 75 liter (20 gallon) tank as:
0.003 ppm
*which is undetectable by most hobby test kits

...and finally, if I read that test plan correctly, looks like that was only "first leech" over 24 hours of un-rinsed carbon. (I won't speculate as to what the results would've been if they rinsed first or re-sampled some days later to see if any additional leeching)

 

[Randy Holmes-Farley Verified Community Expert]

According to this article (Activated carbon comparison) 3 of the brands out of 8, tested as high as 1 PPM while the others were lower by a factor of 4 or more.

Not sure how to translate that to a real world scenario but the article seems to make the findings significant.

I became interested after I noticed I had algae problems increase significantly after a filter change w more carbon then usual. The amount of food I fed was the same.

I doubt the carbon was responsible.

 

[SPS2020]

Welcome to Reef2Reef, norakat.

Thank you Randy...as aways!

 

[Miami Reef]

Wow. We learn something new everyday.

 

[World Citizen]

I made this exact mistake. I tested al the carbon brands in the test vial.
Sure.. they flipped. You would think a Reeftank will die in seconds when adding Carbon.

But when testing in 1 liter of water I noticed it was not that bad. Considering I have over 200 liters over water, we should not be worries about that tiny bit of Po4.

I did learn that no brand has Po4 free Carbon. Name me a brand, I wil test it and eat my shoe.

 

[YOYOYOReefer]

if you are really that concerned and want to run phosphate free carbon, your best bet is to soak your carbon for 4-5 days in ro/di /water , make sure have ozone bubbling in it and to change out the ro/di water a few times in the process.

 

[norakat]

Test you linked was conducted in just 250 mL of water.
I think, to Randy's point, even 1 ppm of Phosphate in 250 mL of water translates into insignificant amounts..

Ok, point taken, but my tank is only 5 gallons and the amount of carbon I use is more than 50ml (which is about 3/4 of a shot glass).

Thanks for the replies