Theory on the role of zeolite in marine tanks .

[alessandro]

For a long time we are debating on the role of zeolite ( clinoptilolite ) in marine tanks with carbon dosing and in particular on the possible reduction of phosphates.
Those who follow systems based on the use of zeolite believes that the zeolite is an excellent substrate for colonize for phospho-reducing bacteria.
These bacteria then , shacking the zeolite would come into circulation in the tank consuming phosphates which would then foamed by the skimmer .
If this theory is correct I do not see why the zeolite should be changed every 30-45 days, but after the change , there should be an increase in phosphates.
Instead, the opposite is true .
Immediately after the change the phosphates decrease, although minimally.
I think p an analysis made ​​in 2002 by Lars Sabrella can help to undestand the processe.
Sabrella analyze the content of the zeolite before being introduced in tank and after the change.

http://www.lars-sebralla.de/ma_zeovit.html

As you can see from the analysis, the iron was down significantly .
Then the zeolite releases iron in the tank.
What I think is that this iron binds to phosphates.
Is it plausible ?
In this case the bound iron phosphate where would you go ?
in the skimmer or in the substrate rocks ?

 

[bertoni]

All organisms require phosphate to grow, so perhaps replacing the zeolite allows more phosphate consumption by encouraging growth. Removing the old zeolite removed the phosphate in the bacteria growing on it, so encourage more biomass could reduce the phosphate level. That's similar to the way that harvesting macroalgae works. Iron is a nutrient required for photosynthesis, although I'm not sure why the zeolite would release iron.

 

[dkeller_nc]

I personally doubt the explanation of how zeolites work in a reef tank that is usually proffered by zeovit aficionados. The typical explanation is that bacteria colonize the surface, and the biofilm that they form is removed by mechanical action. The bacteria in the biofilm is said to both feed the corals in the system, and also is removed by the skimmer, thus exporting phosphate and nitrates.

I don't doubt that bacteria colonize the surface of the zeolite, use both nitrate and phosphate to grow and are removed by skimming, thus exporting nutrients.

The problem is that this is true of any substrate in a reef tank, and it isn't necessary to use mechanical action to slough off bacteria, as any mature biofilm will shed into the water column on its own.

Fundamentally, all zeolites are molecular sieves. They segregate dissolved molecules from the water column by selective diffusion into the material's pores, and exactly what they will remove is largely based on pore size. There is also some possibility of ion exchange, but in a saltwater environment, any ion exchange will be instantly overwhelmed by the high concentration of dissolved ions.

So in my opinion, the zeolites sold for use in a reef aquarium are probably acting as molecular sieves, and it is necessary to mechanically agitate the material to prevent a bacterial biofilm from completely occluding the pores. Once the capacity of the material is exhausted, replacement is necessary.

If they were acting solely as a substrate for bacterial growth, replacement wouldn't be necessary, as you've pointed out. For that matter, they wouldn't be necessary at all, since the surface area of the live rock in the tank would greatly exceed the surface area in the relatively small volume of zeolite typically used.

 

[dartier]

I am also of the opinion that zeolites are directly removing unwanted molecules like PO4. However I suspect that the zeolites are only being used to temporarily lock up PO4, and the bacteria growing on them is utilizing the trapped PO4, freeing up the space in the zeolite material and then the process starts again.

I also seem to remember that zeolites are known to remove Ammonia, which could also be leveraged by bacteria by using it before it could be utilized by Algae.

If that were all that was happening, you would never have to replace it, but a requirement for using Zeovit is to monitor Potassium as the zeolites can strip Potassium. So I would say that the zeolites are not as efficient (or selective) as you would like in what they remove and the removal of benign elements is what causes the zeolites to be exhausted and need to replaced.

As for the iron, glennf in his DSR thread mentions that he doses iron to lower PO4 through bacteria growth (and yes, it can also spur nuisance algae).

Dennis

 

[bertoni]

How does this mechanical action work with zeolites? I haven't heard of that. How long does a batch of zeolite stay in a ZeoVit system?

Some zeolites can bind ammonia in fresh water, but this doesn't happen in saltwater. The ionic content, especially of sodium, is too high. I haven't heard that zeolites can bind phosphate.

 

[alessandro]

How does this mechanical action work with zeolites? I haven't heard of that. How long does a batch of zeolite stay in a ZeoVit system?

Some zeolites can bind ammonia in fresh water, but this doesn't happen in saltwater. The ionic content, especially of sodium, is too high. I haven't heard that zeolites can bind phosphate.

around 45 days.

Yes I know zeolites cannot bind ammonia in saltwater.
I know very well all about zeolite story I put it in my tank in 2002 when Zeovit started to appear in European market.
what I'm trying to focus on is that the analysis shows that the zeolite releases iron in large amounts.
I wonderer if this iron can bind directly PO4 without bacteria methabolism.

 

[dkeller_nc]

How does this mechanical action work with zeolites? I haven't heard of that. How long does a batch of zeolite stay in a ZeoVit system?

Some zeolites can bind ammonia in fresh water, but this doesn't happen in saltwater. The ionic content, especially of sodium, is too high. I haven't heard that zeolites can bind phosphate.

Wikipedia's article on molecular sieves can do a whole lot more thorough job of explaining the differential pore diffusion mechanism that I ever could in a forum post:

http://en.wikipedia.org/wiki/Molecular_sieve

 

[dkeller_nc]

what I'm trying to focus on is that the analysis shows that the zeolite releases iron in large amounts.
I wonderer if this iron can bind directly PO4 without bacteria methabolism.

I think that zeolite provided by Zeovit and other brands targeted to saltwater are all naturally-occurring, mined minerals rather than manufactured molecular sieves. If so, the iron would have to be a contaminant in the matrix, and would also have to either dissolve in the saltwater and then precipitate as iron phosphate, or small insoluble particles would have to be present on the surfaces of the zeolite.

I think scenario #1 is unlikely - most iron oxide compounds are very insoluble in seawater (though not all). The only way to confirm #2 would be to do some chemistry and electron microscopy on samples of zeolite.

 

[dartier]

How does this mechanical action work with zeolites? I haven't heard of that.

The Zeovit reactors have a handle that needs to be pumped causing a plunging action to be performed. In the basic ones it is manual, and in the high end ones it is automated.

As dkeller_nc noted, it is credited with releasing the bacteria from the media.

Dennis

 

[bertoni]

I don't know whether the iron is going to bind much phosphate. If there's much Fe⁺⁺⁺ in the mix, it might. The resulting ferric phosphate should be fairly insoluble (otherwise GFO wouldn't work), so it should precipitate.