Could I make an Anoxic Nexus?

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GDL
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Could I make an Anoxic Nexus?

Post by GDL »

Hi,
As a long term lurker and occasional poster I have watched with interest the many posts on filtration and the changing orthodoxy.

I have a 15000l oval pond with a nexus 200 on the BD. It is currently lightly stocked, but I intend to add more fish this year.
Having read Syd's articles on anoxic filtration I am intrigued by the whole idea, but I do not have room to build one without major construction work.

I wondered if I could create anoxic inserts for my nexus using pond socks (or similar) containing the cat litter and a laterite core hung vertically in the outer part of the Nexus.
The centre part of the Nexus would still provide my mechanical filtering and some bio capability.

With 150mm diameter sock containing about 6l of litter/laterite, I would get about the same in each as a normal anoxic basket.
I think I could get about 15 hung in the nexus, perhaps a few less.

Interested in people's thoughts on the idea.

Cheers
Gordon
Manky Sanke
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Re: Could I make an Anoxic Nexus?

Post by Manky Sanke »

Gordon,

Have you read the latest article I've written about anoxic filtration? Over the past few years I've been asked many questions and I've answered a great many forum posts so the purpose of the article, apart from describing the system in as complete detail as I could manage, was to address all the usual questions. One of the points I've covered addresses the effectiveness of just using a few baskets as an addition to a conventional filter instead of the full recommended number as a stand alone anoxic system. Another point I've covered is that of using baskets in unusual locations, I haven't covered putting baskets (or socks) into a Nexus but the general principles are covered.

As far as I'm aware, everyone who has used the system is pleased with the results and the only people who have reported failures are those who haven't read how anoxic filtration works and have consequently made elementary mistakes. The article is quite long but, rather than a long technical waffle, I've broken it down into sections which describe the various points with the main body of the text being kept as simple as possible and with all the technical stuff in science panels which can be read by those who want to know the science or ignored by those who don't. Have a read and, if you have any questions just ask.

http://www.mankysanke.co.uk/html/anoxic_filtration.html
GDL
Lemon Shark
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Re: Could I make an Anoxic Nexus?

Post by GDL »

Thank you

Actually, it was reading your article that got me thinking and I've been mulling it over for a while.
I'd even thought of trying to put baskets in the nexus, but unlikely to get many in without the 'flow through' rather than 'flow past' problem.

The vertical sausage idea came to me and then the use of a pond sock to achieve it.
Mind you, having seen the price of pond socks, I'm now thinking weed control fabric and a sewing machine :)

I guess I was just looking for confirmation that I hadn't missed the point and I'm not thinking of doing something daft.

I think I'll start exploring the mechanics once I've got the flow thought my airlift returns where I want it.

Cheers
Gordon
Drakoi
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Re: Could I make an Anoxic Nexus?

Post by Drakoi »

I think you might have a problem finding a spot in your nexus which does not have too much flow or too much oxygen ?

Dont forget for anoxic filter is based on low oxygen so that the nasty bugs will break no3.
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Re: Could I make an Anoxic Nexus?

Post by Manky Sanke »

An anoxic basket may not fare very well in a strong current of water because the difference in water pressure between the side upstream of the water flow and the side that's downstream may cause water to flow into the basket. That's all explained in the article on my site. This is a quote from it.

Floating baskets and unusual locations
Biocenosis baskets don’t have to be in a separate anoxic pond if space is limited. They will work just as well in the main pond in floating baskets or in baskets suspended at the surface if this is done in such a way that inquisitive fish cannot excavate them. They can also be put into water features such as streams or rock pools but there are restrictions as far as water flow past them is concerned. They need a non-turbulent water flow so as not to wash the cat litter out of the baskets, either from the top or through the holes in the sides. Baskets in ponds can be protected from being excavated by putting them in the legs of stockings or tights (pantyhose) and tying the tops loosely around any plant stems.

Water doesn’t flow through a biocenosis basket as it does through a media bed in conventional filtration. There is a possible problem if one side of a basket faces a strong flow of water and the opposite side is downstream of the flow. The pressure of water onto the side facing the flow might cause freshly aerated water to penetrate into the basket. Worse still, the differential pressure across the basket might even force water to flow through it. The first scenario would make the basket less efficient, the second would prevent the anoxic environment forming in the centre of the basket. Anoxic filtration is simple, inexpensive and very efficient if you follow the rules but doomed to failure if you start altering the design parameters without having understood the principles.


That would make it impossible to find a spot in a Nexus where the turbulent and non-diffused water flow wouldn't disturb a basket but the fact that the water was highly aerated wouldn't be a problem. Due to biological action, the centre of the basket naturally forms an anoxic environment with dissolved oxygen levels between 0.5 mg/L and 2 mg/L but the environmental water around an anoxic basket can be fully aerated to saturation oxygen levels.

BTW the bugs that colonise the centre of the basket aren't the "nasty" type that proliferate in anaerobic (no oxygen at all) sludge. That's an old myth that was put about by those who opposed anoxic filtration when Kevin Novak first began to promote the system as a suitable filter for koi ponds. I've debated anoxic filtration with a great many hobbyists but I've never found an anoxic critic who had taken the trouble to find out how it works and most seemed not to understand the difference between anoxic and anaerobic.
Drakoi
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Re: Could I make an Anoxic Nexus?

Post by Drakoi »

Manky how long would it take for a basket of anoxic filtration until it is mature?

Also, wont the cat litter fall from the gaps of the basket every time you move it ?
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Re: Could I make an Anoxic Nexus?

Post by Manky Sanke »

It isn't possible to accurately predict how long any biological filter will take to mature since much will depend on water parameters, especially temperature. That said, a biocenosis basket will mature at a similar rate to a conventional biofilter.

As for the cat litter falling through the holes in a basket, if a cat litter is chosen that complies with the recommended specification, the size of the granules will be too large to fall through the holes in a normal planting basket.
GDL
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Re: Could I make an Anoxic Nexus?

Post by GDL »

I would agree on the basket, which was why I was thinking of a fabric sock suspended vertically in the outer chamber of the nexus.
The fabric would prevent the flow through problem, while still allowing water into the media inside.
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Re: Could I make an Anoxic Nexus?

Post by Manky Sanke »

Gordon,

I always appreciate pushing the boundaries of new ideas and I welcome seeing the results of your trials, whether positive or negative, but don't go into this without realising the problems.

The anoxic system was designed to be installed in a dedicated pond where the flow was non turbulent and where there was room for one basket per adult koi. If the baskets also contain plants they will be much more efficient and that arrangement will be a complete replacement for any other form of filtration as they will provide all the biological filtration that is needed. The system will, not only, remove ammonia without leaving nitrate but has some spare capacity to remove nitrate created by the normal nitrogen cycle activity that happens on pond walls, floors and everywhere else in the pond so, apart from mechanical filtration, nothing more will be necessary.

Over time, hobbyists who are attracted to the idea of very low nitrate levels have wanted to "try a few baskets" to see if they can achieve a reduction in their nitrate level. This faces the problem that, in addition to the normal biological activity in the pond itself, the baskets have to compete with conventional filters which are continually pumping considerable amounts of nitrate into the water. If you have sufficient baskets then they can cope with the extra load but if there are only a few baskets, although they will each be helping to reduce the nitrate produced by the conventional filter, there will be too few to make a dramatic reduction.

I don't know which Nexus you have and I'm not sure how many socks you can fit in but each sock will interrupt the intended flow pattern and the idea of installing several might, to use the scientific term, bugger it up completely!

There is another factor to consider. The whole principle of anoxic filtration is that an anoxic environment is maintained inside zone C. When the baskets are first submerged, oxygenated water will flood in but the oxygen level will deplete over a few days by nitrogen cycle bugs in zones A and B. As the oxygen level reaches about 0.2 mg/L, one my favourite expressions takes place: :twisted:

Facultative anaerobic chemolithic bacteria have a dimorphic metabolism and, under anoxic conditions, their respiration will switch from aerobic respiration to fermentative respiration. :shock:

That means that these bugs prefer the "breathe" oxygen when it is available but will switch to a process that steals the three oxygen atoms from nitrate (NO3) in the water which removes it from the environment by converting it to nitrogen gas (N). Actually to be more accurate for the sake of people who understand chemistry, two of thes Ns then combine the make di-nitrogen (N2) but it amounts to the same thing - nitrate is removed by converting it to dissolved nitrogen which bubbles away to the atmosphere.

Below is an extract from my anoxic filtration article where I addressed the situation of draining anoxic ponds too frequently. Occasionally will cause no harm because anoxic conditions will soon return but it shouldn't be done too frequently or the baskets will always be playing catch up rather than getting on with doing their job. Relating this to putting baskets or socks into a Nexus means that they will be drained weekly or more often, which will probably mean that they won't be able to function.

"When cleaning the anoxic pond, a point to bear in mind but which shouldn’t be exaggerated is that, if the anoxic pond is completely drained or if a biocenosis basket is removed from water, the oxygen depleted water in zone C obviously will drain out. The water in the basket won't immediately drain completely; some oxygen depleted water will remain inside and will only drain slowly if the basket is left out of water for too long. When the pond is refilled or the basket is resubmerged, the anoxic environment will be removed as aerated water floods back in.

The anoxic environment will soon be restored but, depending on how much water had drained out and therefore how much aerated water goes back in, the interruption will either be a short blip or, in the case of a complete dry out, it may take much longer. Interrupting the anoxic environment will only be a significant factor if the baskets are left to drain for too long during cleaning or transferring to another pond so that all the oxygen depleted water drains out. I don't see a problem arising from cleaning the anoxic pond provided it isn't done every week."


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