Anoxic filter

[Bribe1961]

Hi
I'm in the process of building a new pond and am really intrigued with the anoxic filter.
Does anyone have one, if so are they all their cracked up to be, also could this be the only filter you need. With what I have read they seem to be a great way forward,but I'm sceptical.
Tia Brian

[MCA]

<p>
This goes back to designing a pond filtration system. An anoxic environement (not a filter as it does not filter out anything) is one way or encouraging denitrification/mineralization of nitrates by having bacteria break apart the nitrate molecule to consume the oxygen and release the left over nitrogen as a gas. But talking first about nitrate processing is putting the cart way too far in front of the horse. Pond water processing:

• Stage 1 Mechanical: This is where we bring the water out of the pond to a filter pit via gravity (preferred) or pump from bottom drains and skimmers. We cause the water to go through one or more barriers that trap and hold the undissolved solids. One of the best ways to implement the mechanical stage is via rotary drum filter (RDF) as those can filter down to the 50micron level and are self cleaning. The negative for an RDF is the capital cost. Maybe second best is a parabolic sieve made of edgewire with a 200micron gap. This is a small amout of maintenance with these. Next best may be a static bed of something like micro K1. Such static beds are easy to clean by boiling the media with air and dumping the water.
• Stage 2 Nitrification: The mechancally clean water is introduced to media in a O2 rich environment where naturally occuring bacteria secies with convert ammonia to nirite to nitrate. It is very hard to beat a shower with ceramic media for doing this work. Second best choice might be a fluid bed of micro K1.
• Stage 3 Denitifcation/Mineralization: This final stage can be considered optional and used, along with water changes, to hold down the nitrate levels. A very good device for this purpose would be a traditional bead filter. Being a presurrized chamber the only O2 introduced is what is dissolved in the water. So the environment can support denitification/mineralization. A side benefit is that the bead pack can also do water polishing and help trap any small solids.

</p>

[MikeM]

It has been a very long time since I heard any hobbyist claiming success in relying on anoxic "filter baskets". I know a fellow who installed some and continues to have it, but he is careful to say he is unsure if it does any good.

The theory behind them is sound, but koi ponds produce so much ammonia/nitrite/nitrate on a continuous basis that it is impractical, IMO, to think all that water volume is going to come into contact with the clay sufficiently rapidly to allow the koi to be in ammonia/nitrite/nitrate free water. The bottom line is that water changes remain essential to maintaining water quality. If the hobbyist is in an area with water restrictions, any little bit of benefit reducing the amount of water used can become a big deal. But, I tend to think the biggest benefit of anoxic filter baskets has been from giving the hobbyist a sense that they are trying everything to minimize water use, reducing their sense of guilt in how much water they use.

[MCA]

But does anoxic reduction of nitrates solve all the other issues addressed with lower amounts of water changes such as: declining KH, increased GH, declining ORP due to increasing amounts of organics in the wate column? To me solving high nitrates is very low on the bucket list compared to other issues. Standalone anoxic bioconversion of nitrates (not filtration) is the tail wagging the dog.

[MikeM]

I agree. Only water changes deal with the full range of parameters involved in maintaining water quality. I would not minimize the benefit of lowering nitrate levels, but at the same time think most hobbyists should consider nitrate as a marker for all the factors involved in deterioration of water quality. It is easily detected and measured. Other factors are not so easily tested. When nitrate is targeted by de-nitrification, resin capture, clay capture or some such, it no longer serves as a marker for all the rest. Good to be rid of it, but there is still everything else.

If I was in an area with strict water use limits, I would experiment with "water rejuvenation" with PP treatments/ozonation in a water storage system outside the pond, but even then I would be wondering what was missing that I could not detect.

[MCA]

<p>
I agree about lowering water usage. We should be able to minimize water change for a given stocking and feedling level by use a excellent mechanical stage (RDF comes to mind) with a counter current factionator using O3 to keep the ORP in the 375mV range. Then run that water to a shower for aeration, gas exchange, and any needed nitrification/denitificiation. Would need to add cabonates to keep KH well north of 100ppm and ph north of 7 and stable.</p>

[John Seifert]

I am using 3 filtration systems, Kaldness moving bed (8,000gph), 2 showers 3,000gph each), and anoxic (6,000gph) . All have separate mechanical filters. The anoxic has 36 baskets, no plants. Pond is 14,000 gallons. Before adding anoxic, my nitrates were running 60ppm+. Within 3 weeks of installing, nitrates about 10, currently under 5. I do about a 5% flow-thru water change per day with source water at 3ppm nitrates. I installed the anoxic 2 years ago, very low maintenance. I am considering replacing the showers with anoxic.

[MikeM]

On my pond there is moving bed kaldnes (Nexus filters), shower filter and a bead filter for capturing fines. Weekly water changes are approximately 35%, but sometimes less during the parts of the year when not dealing with falling leaves, pollen, etc. My goal is to have nitrate not exceed 5ppm, and generally succeed in having it less than 5ppm. Accurate measurement of nitrate below 5ppm is a challenge, so I'd hesitate to say anything more. I feed approximately 1.25 pounds of high protein food per day in 12,500 gallons of water.

You are getting like results with 5% daily flow through of fresh water, which is roughly equivalent to my 35% weekly. The main difference seems to be that your fresh water has 3ppm nitrate, while mine has some undetectable level. The anoxic baskets may be having some beneficial effect, but it would be hard for me to reach a conclusion of what that impact is.

It will be interesting to see what changes occur if you go forward. However, why eliminate the shower? Just add more baskets and see what effect that has. There are a considerable number of reports suggesting that the degassing of ammonia by showers could be as much as 10% or so, depending on climatic factors and such, or the equivalent of a 10% water change. In some conditions, however, the degassing can be minimal. In nearly all applications, showers are tremendously oxygenating, a benefit not to be overlooked. If the only change is adding baskets and doing so has a measurable impact, you will know what it is. If you want to turn off the showers later, you can always do so.

Let us know what you learn.

[MCA]

I am considering replacing the showers with anoxic.

How can nitrification in the relatively O2 rich world in a shower be replaced by de-nitification/mineralization in O2 deprived anoxic environment? I do understand how one set of processes with different inputs and outputs can replace each other. Output of nitrificaiton is nitrate. Output of de-nitirication/mineralization is nitrogen gas after the bacteria steals and consumes the O2 atoms from the nitrate molecule.