Po4 binding capacity of steel(wool)

[Timmste]

I wondered how much Po4 is bound per gram of steel. In one of my tests I reduced Po4 by 0,04 with 1gr of steelwool per 400l aquariumwater. In another test.. Po4 rose to 0,12 and it took me 8gr of steelwool to lower Po4 to 0,08.. approximately 0,36 should have leached out of the rockwork..

But I wonder if there is a is a way to actually calculate the phosphate binding capacity of steelwool.

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[bertoni]

I don't how to do that other than experimentally. The surface area is the difficult issue, since that determines how much can be bound. In theory, someone could add known quantities of phosphate to a water sample and circulate it for a while to get a rough idea. Note that the binding amount might tend to increase as the concentration increases, though. I'm not sure how large the effect might be.

 

[Timmste]

I don't how to do that other than experimentally. The surface area is the difficult issue, since that determines how much can be bound. In theory, someone could add known quantities of phosphate to a water sample and circulate it for a while to get a rough idea. Note that the binding amount might tend to increase as the concentration increases, though. I'm not sure how large the effect might be.

Why is the surface area difficult? The steelwool rusts and falls apart after a day or so. I leave it in there and it will disappear eventually, it takes a few days/week.

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[Timmste]

I guess when it turned into a powder that is the best time to check how much Po4 is left?

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[bertoni]

I think I am not communicating well.

If you want to estimate the amount of phosphate removed by the medium, you'd need to estimate the surface area. If you'd like to determine experimentally the amount of phosphate the medium can bind, then treating some amount of water and doing the math would be fine. With rock in the tank, you'd also be guessing as to the amount leached from the system. Taking a water sample and treating it in a separate container would be more accurate, I suspect.