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Alfagrog for reducing Nitrates?

Mxx

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Does Alfagrog have an appropriate porosity for growing decent amounts of anaerobic bacteria, in order to remove nitrates? (Just as live rock does in reef aquariums, or media such as Seachem Matrix do).

I'm guessing it perhaps does, but it would be good to have some confirmation of this before I try to depend upon it for doing so in a sump, in case anyone else has found this information previously!
 

dw1305

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Hi all,
It may dependent upon the size of the alfagrog lumps, how closely packed they are, and how much O2 is entering the filter. Personally I don't think there is any point in closed cell plenums, de-nitrifying coils etc. They are really fiddly to get right, and in my opinion it is much better to try and keep all the filter material aerobic and use plants to mop up the NO3. Even if I didn't have plants, I'd still use water changes rather than trying to out-gas the N2.

With apologies for the cross-post, but have a look here: <http://www.plecoplanet.com/forum/showthread.php?t=11898> & <http://plecoplanet.com/?page_id=829>.

cheers Darrel
 

Mxx

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That was my second potential question, which alfagrog grain size would be best.

For anaerobic bacteria I don't believe the flow rate and the oxygenation are that critical. Flow will happen at the lump surface, but the anaerobic bacteria would be residing deep within the lump where the flow would be very slow and the oxygen would already be consumed by the aerobic bacteria. growing closer to the grain surface. Different grain sizes and flow will just result in the anaerobic bacteria growing slightly closer to or further from the grain's surfaces.

I looked into denitration coil filters but they do sound tricky, require maintenance, and can even be dangerous to your stock. Denitration media is basically zero-maintenance though and foolproof.

I definitely do want to filter out nitrates regardless. My reasoning for that is a little complicated. I'm next planning to do a large hybrid high-tech/low-tech system with a low maintenance approach while trying to achieve optimal water conditions. So if the plants are using the nitrates, and then if I'm not pruning and am allowing the leaves to decompose naturally as I'm already mostly doing happily now, then that nitrogen will just be perpetually reintroduced back into the water. I'm intending to keep the water as lean as possible while using a soil substrate continuously replenished through perforated substrate manifolds via a peristaltic dosing pump drip. So nitrates should be in non-limiting in the substrate continuously, while any that make it into the water would rapidly be removed by a large amount of anaerobic bacteria. So regardless of the water changes schedule, I shouldn't have nitrates accumulating to any amounts in the water while the plants would not be limited, and wouldn't have to worry precisely about dosing amounts or whether there is an excess there which is affecting the fish. That's the idea anyway!

Alfagrog looks like a very good value in any case, if it does in fact absorb nitrates sufficiently. I'd seen it mentioned by reefers, but not in any detail in regards to it's effectiveness for such. It's a lot cheaper than Seachem Matrix or other similar media, but I could use those if the alfagrog isn't going to work well though.
 

dw1305

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Hi all,
For anaerobic bacteria I don't believe the flow rate and the oxygenation are that critical. Flow will happen at the lump surface, but the anaerobic bacteria would be residing deep within the lump where the flow would be very slow and the oxygen would already be consumed by the aerobic bacteria. growing closer to the grain surface...........My reasoning for that is a little complicated. I'm next planning to do a large hybrid high-tech/low-tech system with a low maintenance approach while trying to achieve optimal water conditions. So if the plants are using the nitrates, and then if I'm not pruning and am allowing the leaves to decompose naturally as I'm already mostly doing happily now, then that nitrogen will just be perpetually reintroduced back into the water. I'm intending to keep the water as lean as possible while using a soil substrate continuously replenished through perforated substrate manifolds via a peristaltic dosing pump drip. So nitrates should be in non-limiting in the substrate continuously, while any that make it into the water would rapidly be removed by a large amount of anaerobic bacteria.
I understand your reasoning, but I think the concept is basically flawed. In a closed system, like a canister filter, it is almost impossible to get the balance between aerobic/anaerobic. You could however do something similar in a system open to atmospheric oxygen. This is a schematic from a trickle filter dealing with waste water (landfill leachate in this case), and using an alfagrog type media.

trickle.jpg

(from <http://plecoplanet.com/?page_id=829>)

But even this system would need occasional cleaning to stop the bacterial layer from becoming too deep. The efficiency of the nitrifying bacterial metabolism depends on a large water surfaces exposed to oxygen (the “Gas Exchange Capacity”), this is because the nitrifiers compete poorly for oxygen with the community of bacteria that are breaking down the organic matter, the ones responsible for much of the biochemical oxygen demand (BOD). You can make use of your sediment to some degree, because the uppermost surfaces of the substrate are a good location for nitrifying bacteria, mainly because the nitrification process uses a lot of oxygen. However only a few centimetres below the substrates’ surface, the diffusion of oxygen can't supply enough oxygen, and as oxygen levels fall anaerobic bacteria become more frequent (in exactly the same way that is shown in the schematic drawing of a cross section of a trickle filter). Many of these bacteria are in fact “facultative anaerobes”; when oxygen is in short supply, they are able to switch to a metabolism that doesn't require oxygen, instead, they use nitrate, stripping the oxygen and leaving nitrogen (N2) gas. The nitrifying bacteria provide the nitrate, and their high oxygen demands also tend to exhaust the limited supply of oxygen. These two types of bacteria will occur across a fluctuating boundary lying not far beneath the surface of the substrate. The same processes will also occur in the “rhizosphere” the aerated zone lying around aquatic plants roots. I agree with you that these processes are both a good reason for both having a substrate, and leaving it relatively undisturbed.

In a canister filter, inevitably as the flow speed drops, the oxygen in the water won't meet the oxygen demand from the bacteria inside the filter. There are 2 components of this biological oxygen demand(BOD), "ordinary" decomposition:
Oxidizable material + bacteria + nutrient + O2 ? CO2 + H2O + oxidized inorganic such as nitrate (NO3) or (Sulf(ph)ate) SO4.
and "nitrification": NH3 + CO2 + 1.5 O2 ? NO2- + CO2 + 0.5 O2 ? NO3-

Simply stated, a heavy load of organic materials being degraded in your system inhibits the nitrifiers by competing with them for oxygen. Dissolved oxygen concentrations above 1 mg/l are essential for nitrification to occur. If DO levels in the filter drop below this level nitrifications slows, or ceases altogether, the NH3 passes through the filter without entering nitrification and the fish experience high NH3, low O2 conditions in the tank, with potentially catastrophic effects.

I think you can have a system where you do very maintenance (I do very little), but you need to keep the filter media aerobic.

cheers Darrel
 

Greg's Pea

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Totally agree with the above sentiments. Used to be an industrial microbiologist and in my experience you'll be tinkering for eternity trying to do what the plants can do for you.
 

dw1305

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Hi Shaun,
Totally agree with the above sentiments. Used to be an industrial microbiologist ....
That is very interesting, can you tell us a bit more? I come from a botanical background and I only know about the bits of microbiology that I've encountered during work.

cheers Darrel
 

Greg's Pea

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dw1305 said:
Hi Shaun,
Totally agree with the above sentiments. Used to be an industrial microbiologist ....
That is very interesting, can you tell us a bit more? I come from a botanical background and I only know about the bits of microbiology that I've encountered during work.

cheers Darrel


Hi Darrell,

I still wish I was more into plants when studying myself. Wasting education on the young, bloody rediculous.

When I was running the lab we would always come up against the same problems. We would build a biochamber on site to grow and utilise Nitrobacter & Nitrosomonas for waste water cleaning. These bacteria will grow like mad under a wide range of conditions.

The problem though was always 'contact time' and 'oxygenation levels'. Hitting that sweet spot of slow enough flow to allow the bacteria to do their 'job' with enough airation was hard. We would mostly resort to a huge airstone in one of the sumps. The amount of times I've wondered how this could be incorporated into a canister filter.....

We also used to sell pure cultures to 'pond folk'. Their NH3/NO3 problems would be instantly resoved upon addition of the bacteria but over time their levels would fall again and the problems would arise once more.

Anaerobic digestion has always intrigued me but large scale installations just aren't done in this country. The dutch on the other hand love AD and i'd be very interested to see its application to the hobby more.

But it still seems to fall back on what you experienced guys keep telling us. It might be a quick fix but it's usually trying to mask an issue that is present (overstocking, underfiltering, poor flow) and since it won't really solve the root cause he'll be back at some point to rear his head.

I realise I've tangented about the shop with my description there but hope it was of some interest.

Cheers

Shaun
 

dw1305

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Hi all,
My nitrates are rarely over 10ppm due to plants
I think that would be a fairly general finding for most of us who don't use heavy fertilization regimes and have a reasonable plant mass. Nitrogen is often the limiting nutrient in natural ecosystems, so plants have evolved to be extremely efficient at taking it up.

This is partially why I don't think you need to look any further than a filtration system where the biological media is all aerobic, converting NH3 + CO2 + 1.5 O2 ? NO2- + CO2 + 0.5 O2 ? NO3- and then using plants (particularly ones with access to atmospheric CO2) to mop up the NO3.

cheers Darrel
 

ceg4048

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Hi Darrel,
Actually I believe that in most natural systems, Phosphorous is the limiting nutrient since it is so energetic that it bonds easily to form insoluble compounds. As a result of it's intrinsic energy PO4 is THE principle ingredient of the important nucleoside ATP - and ATP is often referred to as the energy currency of living cells, so PO4 is highly sought after. N is fairly easy to come by, comparatively, as there are plenty of things rotting in the sediment which liberate N.

Cheers,
 

Mxx

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However, if for instance you're running a low-light tank as I am, then you're likely not having intense plant growth which requires pruning all the time. Accordingly, if you're not removing lots of plant mass frequently, then that nitrogen in the plants is still going to remain in the tank's system and will be released again once the plant leaves get replaced and decompose naturally (as I'm letting them do, and no that does look fine as it's all behind the driftwood barrier anyway).

Anaerobic decomposition of nitrates tends to happen to some degree in any tank, with the nitrogen gas then off-gassing. (Diana Walstad reports in her experiments that I believe close to 30% of the nitrogen put into a tank system over a month could not be accounted for by other means such as plant mass which means that it must be getting anaerobically reduced in the substrate and then off-gassing). But you can increase or decrease the amount of aerobic decomposition as well as you like through various means such as how exact;u you do your substrate or if you use a filter medium like Matrix.
 

dw1305

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Hi all,
Actually I believe that in most natural systems, Phosphorous is the limiting nutrient since it is so energetic that it bonds easily to form insoluble compounds.
Point taken, probably should have said "one of the.....". Phosphorus is definitely the limiting nutrient in a lot of aquatic systems, for example this is why there has been problems from the optical brighteners in washing powder in the UK.

This ability to form insoluble compounds (for example calcium phosphate complexes), and to be strongly bound to clay minerals actually becomes part of the problem, with many sediments now having phosphorus loads that will take thousands of years to deplete naturally.

Optical brighteners are slightly unusual in that in most cases of pollution from agricultural fertilizers or sewage works high N and P levels go together. <http://pubs.acs.org/doi/abs/10.1021/es202401p>

Lewis et al. (2011)
"Rationale for Control of Anthropogenic Nitrogen and Phosphorus to Reduce Eutrophication of Inland Waters"
Concentrations of phosphorus and nitrogen in surface waters are being regulated in the United States and European Union. Human activity has raised the concentrations of these nutrients, leading to eutrophication of inland waters, which causes nuisance growth of algae and other aquatic plants. Control of phosphorus often has had the highest priority because of its presumed leading role in limiting development of aquatic plant biomass. Experimental evidence shows, however, that nitrogen is equally likely to limit growth of algae and aquatic plants in inland waters, and that additions of both nutrients cause substantially more algal growth than either added alone.......

cheers Darrel
 

Spacehooter

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I have a 330ltr tank with an FX5 filter loaded with crushed Alfagrog in net bags. also I have about a large saucepans worth of uncrushed Alfagrog in the tank at the end where the water enters. It was stacked into a cone in one corner but the fish have spread it around a bit at one end. I have 0 nitrate in my tank. I thought it was a problem with my test equipment but later confirmed that it was indeed zero. I had previously had many problems with my old setup, but with the arrival of the FX5 I decided to go with Alfagrog. I have 5 Koolie loaches, 5 corys, 2 Golden loaches, 1 neon, 1 Angelfish (responsible for number of Neons) 8 Zedras, 6 Mountain Minos, 1 Bumblebee catfish, 1 rainbow, 5 Silver sharks 5", 9 Silver dollars 4", 5 Spotted Silver Dollars 3", 1 10" plec, 1 Bristlenose, 5 Clown loaches 3" and a load of other random fish that I don't know the name of. Normally I don't have this many fish but A friend gave up his tank due to a house move and gave me all his fish. When he did my tank started to cycle again in order to deal with the increased bio load, and sure enough 4 weeks later my nitrates disappeared again. I keep my tank at 26 degrees and with a PH of 7-7.2. I add precipitated chalk to my tank to boost PH as the water in Cornwall tends to have a low ph with no buffering meaning the ph can drop from 7.2 to 6.4 in a couple of days. Below 6.4 the biological system starts to shut down and die off. it requires a PH of over 7 even up to 8 to be most effective so I struck a compromise at 7-7.2 for the fishes sake. All my levels for Ammonia, Nitrite and Nitrate are un-measureable. I recommend Koolie loaches in your tank if you take my approach as you will never see them and they constantly live and clean the Alfagrog. Also I have almost no sign of algae and no plants at all.
 
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I used Alfagrog in an Ehiem external but found it did clog up quite quickly so I switched to ceramic tubes. It's a trade off between how much surface area you need x water flow and how often you want to clean the filter. Looking at the charts nothing comes close to Alfagrog in terms of surface area.
 

dw1305

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Hi all,
I have 0 nitrate in my tank. I thought it was a problem with my test equipment but later confirmed that it was indeed zero. I had previously had many problems with my old setup, but with the arrival of the FX5 I decided to go with Alfagrog. I have 5 Koolie loaches, 5 corys, 2 Golden loaches, 1 neon, 1 Angelfish (responsible for number of Neons) 8 Zedras, 6 Mountain Minos, 1 Bumblebee catfish, 1 rainbow, 5 Silver sharks 5", 9 Silver dollars 4", 5 Spotted Silver Dollars 3", 1 10" plec, 1 Bristlenose, 5 Clown loaches 3" and a load of other random fish that I don't know the name of.
&
Below 6.4 the biological system starts to shut down and die off. it requires a PH of over 7 even up to 8 to be most effective so I struck a compromise at 7-7.2 for the fishes sake. All my levels for Ammonia, Nitrite and Nitrate are un-measureable. I recommend Koolie loaches in your tank if you take my approach as you will never see them and they constantly live and clean the Alfagrog. Also I have almost no sign of algae and no plants at all.
"Spacehooter" I'm seriously worried about the welfare of your fish, have you read the whole of this thread?

You can only remove nitrate (NO3) in 2 ways in a non-planted tank, via water changes, or the anaerobic de-nitrification of NO3 to N2 gas. Looking at your bioload, unless you do a very large water change every day with nitrate free water, your test kit is still wrong. Despite what you may read on other forums etc. it is fairly difficult to measure nitrate levels in the tank, even with analytical grade equipment. I would go as far as to say in my opinion it would be impossible to have no nitrate in this set up.

I would predict that your lack of algae is due to the light levels being too low to support plant growth. Unfortunately because anaerobic de-nitrification is difficult to regulate, and your substrate (or alfagrog pile) must have a large Redox potential, I think and that you are extremely likely to suffer fish deaths fairly soon as your Sharks and Silver Dollars grow, even if you do frequent water changes.

cheers Darrel
 
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dw1305 said:
Hi all,
My nitrates are rarely over 10ppm due to plants
I think that would be a fairly general finding for most of us who don't use heavy fertilization regimes and have a reasonable plant mass. Nitrogen is often the limiting nutrient in natural ecosystems, so plants have evolved to be extremely efficient at taking it up.

This is partially why I don't think you need to look any further than a filtration system where the biological media is all aerobic, converting NH3 + CO2 + 1.5 O2 ? NO2- + CO2 + 0.5 O2 ? NO3- and then using plants (particularly ones with access to atmospheric CO2) to mop up the NO3.

cheers Darrel

Thanks for fixing my typo ;)
 
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dw1305 said:
Despite what you may read on other forums etc. it is fairly difficult to measure nitrate levels in the tank, even with analytical grade equipment. I would go as far as to say in my opinion it would be impossible to have no nitrate in this set up.

cheers Darrel

This brings me to a question I've been pondering since yesterday, I hope this isn't too off topic. Having looked through my water company's quality report apparently nitrates are at 25ppm on average yet my home test kit gives readings of 0 - 5ppm from the tap. I'm now concerned that the nitrates in my aquarium are actually higher than the test kit is telling me, or at least I have no real idea what they actually are!
 

dw1305

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Hi all,
Having looked through my water company's quality report apparently nitrates are at 25ppm on average yet my home test kit gives readings of 0 - 5ppm from the tap.
Could well be the test kit, the only real way to find out would be to add a known amount of nitrates to your tap water, you could do this with KNO3, and then re-test.

The other factor would be the nitrates source, levels will tend to be lower in winter in water drawn from rivers etc, particularly if the source is agricultural. You would really need the range of values. You may find it varies from below 5ppm to 50ppm through the year, with 25ppm the average.

cheers Darrel
 
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