Anoxic filtration

[Airlite]

Syd/Dave, thanks fella's - I'll bear all that in mind and let you know how I get on. Best Regards, Mick

[Airlite]

Hi Chaps. Update; you'll remember that I was thinking about making the jump from "conventional" to anoxic filtration. Well, it's slow going due to work commitments and the fact that I'm a DIY biff but I've made a start. The timber frame for my 6' x 2.5' x 2.5' pool is built and sitting on a similarly constructed timber "stage" in order to raise the base of the pool by 13" or so - that's to give me the option of allowing the filtered water to flow back to the main pond under gravity if I decide to do that (which I will if I can get it to flow fast enough). The box welded liner has been delivered, as have the 20 baskets and the laterite substitute (JBL aquabasis plus). I'll get the cat litter this weekend and start making up the baskets - I was thinking of placing a few of these, once they're made up, into my pond (suitably covered and protected from the fish of course) in order to start them off - is it worth doing that or would it be more trouble than its worth?

My biggest dilemma at the moment is what pre-filter to go for! I've decided that Dave is right and a decent RDF system is going to be my best option, it's just a question of deciding which one! I was originally attracted to the new Oase ProfiClear Compact drum which incorporates the drum element and a small fluid bed bio chamber (overkill I know, but I was 'edging my bets a bit). Anyway, after looking into it, the gravity fed system that I prefer is currently out of the running as my maximum pond water level is just an inch or so too low and to make it work properly would be too much of a pain in the ass(agi)! So now I'm looking at all the other entry level units on offer including the Dracodrum (if their standalone unit is released imminently like their website suggests), the Quinikoi QK22, ProfiDrum 45/20 or Aqua Drum 25 Basic. The QK22 looks best value but I can't find an independent review or video on its performance that would just persuade me to make the purchase. For £200 more the other two come into the equation but it'll be that much again at least in order to get the required pumps, bells, whistles, pipes and connectors and I'd be pushing hard against the financial buffers which I have to take account of as we're having other (arguably more important) work done on the house. The reason I'm set on an RDF is because I installed a couple of lights in the pond a few weeks ago and having switched them on at night (like you do), I saw for the first time exactly how much crud just floats around suspended in the water! I mean, my water looks clear enough during the day but with the lights on at night it looks as thick as treacle! I'm exaggerating of course, but you know what I mean.

Anyway, until I decide what drum is going in I'm going to make sure the pool frame is strong enough to cope with the tonne or so of water it'll have to hold and try to figure out the best way to plumb it all together. Time to study Manky's article again! I'll let you know which drum gets the vote and how the anoxic filter project progresses. Best regards, Mick

[Manky Sanke]

Yes, if you can make the baskets and put them into the pond somewhere it will allow them to begin maturing. As for a prefilters a RDF is very suitable. Let us know how you get on with the one you choose.

[Dave Collins]

Hi Mick,

Can't you sink the drum in the ground a bit so you can gravity feed and then pump the clean water into the Anoxic filter

Have you seen this one ? http://www.koi.jpn.com/shop/filters/bri ... 00-details

[Airlite]

Hi Dave,

Re sinking the RDF into the ground; Nah, the filters live in the garage and it's a concrete floor - I'm not chipping out any of that just for the Oase when there's others that do the job equally well. As it happens, I sent an email earlier this week to Select Nishikigoi Intl and got a reply from Paul who sent me the installation manual for the BD300. I've also been in touch with Mike from QuiniKoi about their QK22 and Tony from DracoDrum asking him when their new standalone unit is due for release (mid May it looks like). I'm still torn between them as I haven't seen one (of these models) up close (can't find a local stockist near me and I don't know anyone personally who's got one) so I'm researching at arms length and relying on t'internet forums and YouTube which is not exactly the most reliable way to judge how you spend the best part of two grand but it is what it is.

I can't remember if I've explained my set-up previously, forgive me for repeating it now if I have. I've got a small, unheated, back-yard pond averaging a fraction over 3ft deep and currently holding 1417 gallons (if I've done my sums properly). I've got a low-end Oase pump (rated around 3500l/h off the top of my head) that feeds a small stream feature that incorporates an alfagrog bed and a few marginal plants to provide a small element of bio/veggie filtration (but mostly it stops dead holly bush leaves being washed into the pond). Needless to say, I've not got a skimmer . The pond wall butts up against my garage so my current meagre filtration system consists of a small two-chamber ERIC type filter (16 brushes in the first chamber, layered jap mat and a final layer of fine filter matting in the second) gravity fed via 4" pipe from the bottom drain. There's another small Oase pump that pushes the filtered water through a 25W Yamitsu UV and back into the pond just under the surface with air provided by a venturi. I don't know the flow rate but it pushes a fair whack through and, along with the stream entering, generates enough of a current to gently circulate the water all the way around the pond. It's probably better if I show you what I'm on about so, on the premise that a picture paints a thousand words, here's a couple that hopefully helps puts the description above into some sort of context:

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Like I've said elsewhere previously; there's no prize winners in my pond. They're mostly low quality, garden-centre specimens but they're friendly and a couple of them are due for their fishy bus passes at 25 yrs old or so. My water parameters are surprisingly stable and have been since the filter matured in the autumn. pH = 7.5; NO2, NO3 and NH4 all 0 or as close to it as you can tell with the limitations of the test kit colour chart.

So why do I want to upgrade to a RDF and an anoxic filter if my water's ok as it is? Well, as small as it is, it takes me around 2-3 hrs each week to clean the filter and associated gubbins. That's time I could use doing other things to be frank! Another reason is the amount of fine particles that I have floating around makes the pond water look like soup when the lights are on. The third is that I worry the current filter won't be able to cope with much more of a load on it and I'd like to add one or two higher quality specimens to my collection in the future. Nothing big or too fancy, but I'd like to see them grow in time and I just think the anoxic filter is a simple and elegant solution which would also be easier and cheaper to adapt than installing something along the lines of a new Nexus or even a home-built K1 fluid bed system. The new frame is big enough to add another 233 gallons (again, assuming I've done my sums properly for a volume of water at 6' x 2.5' x 2.5') which I think will be big enough to take 20 stacked biocenosis baskets. I plan to pump the water from the RDF to the anoxic pool which I've raised so that the max level of water in the pool will be a smidge over 12" above the max water level in the pond (which I hope will be high enough to generate a reasonable flow under it's own pressure back into the pond.

I haven't got to grips with "flow rates" yet. To be honest, I haven't a clue how these are calculated. I know I'll have a total of 7500 litres of water (pond, stream and filters) and this will need to be pushed through at least once every hour but I don't know how much to allow for loss due to pipes and their bends, length, width or height. Would that even be a consideration in my case? There are a number of pumps available that say they'll work up to 1650 gph which sounds about right (I'm thinking of the Oase Aquamax 8000 off the top of my head) but if I put a much bigger pump on, say something like 2900 gph which presumably pushes almost twice the volume of the pond through in that time, would that be too much, too fast? Will the water loiter in my anoxic filter long enough at that rate for the baskets to do their stuff? What is the ideal "flow rate"?

There's a lot still to learn about this hobby. I'd better stop rambling on and get some kip - maybe the answers will come to me in my sleep. Better still, you guys with all your accumulated knowledge and experience, might point me in the right direction? I live in hope. Best regards as always, Mick.

[Manky Sanke]

Flow rates on a pond are difficult to calculate because the manufacturer's rated flow will have been tested under ideal conditions with minimum pipework and with no head to pump against like this



When you put a pump into a practical filter system then every metre of pipe, every fitting used and the friction losses in all equipment will contribute to the overall friction loss and therefore the total loss of flow. If you want to know the turnover of your system, and if it's practical of course, the best way is by accurate measurement. Unless the return is an "over the wall" pipe that could easily be diverted into a dustbin or large container without a significant increase in head loss, the only way might be to divert the flow from the last accessible length of pipe into a container, measure it there and assume that no significant extra loss will occur in the normal pipework back to the pond.

However, with all that said, I'm not a slave to flow rates through biological filters whether they are conventional or anoxic. Provided the media can support sufficient biology to keep up with the ammonia and other pollutants from the fish in the pond and the overall turnover is about one hour or less then, what the bugs cannot get on the first pass of any particular drop of water though the biofilter, they will get on the second. The background level of pond ammonia and other pollutants will not build up, they will reach the same near zero equilibrium regardless of the actual flow through the media!!

This is a very difficult concept to explain and there will be many who say that, if the ammonia output from a biofilter isn't zero then what goes back to the pond will cause the pond level to slowly build up. This is a misunderstanding because the only way to achieve this would be to slow down the flow through the filter so that the bugs would have the time to remove every polluting molecule. But this would slow down the pond turnover and, while the bugs were removing every polluting molecule in the filter system, the fish would be excreting more into the pond. So, in the pond, where it really matters, there would be a higher level than if there was a faster but slightly less efficient flow rate through the biofilter.

[Airlite]

Thanks Manky, I won't get too hung up on the flow rate then and so long as I'm turning the pond volume over at least once every hour the bugs will do their stuff.

[Airlite]

Manky, just a quick question for you if you don't mind me asking. With reference to the Anoxic Filtration article on your website, when making up the biocenosis baskets you have a couple of diagrams that suggest the placement of the laterite, or JBL Aquabasis Plus in my case, goes in the middle of the basket (so a layer of cat litter on top?), but in the opening few lines of your article (para 2) you mention just scooping out a depression in the cat litter and filling that with the laterite. Which is your preferred method or does it not make too much difference? Thanks Syd, M

[Manky Sanke]

If you read that opening expression in it's context rather than take it too literally in isolation you should see that was a hook to intrigue readers so that they would be tempted to read about a form of biofiltration that many would otherwise have thought too technical and boring and which had no place in a "proper" koi pond anyway.

In reality, the exact placing of the laterite isn't crucial so it could be poured into a deep depression in the cat litter but the best performance from a biocenosis basket will be obtained when it's in the centre as shown in the diagrams that show how to make a basket.

[Airlite]

Ha ha, thanks Manky - the hook certainly worked for me!! Centre of the basket it is then. Thanks again, M

[Airlite]

Update: Not much progress I'm afraid The weather's been rubbish most of the week and I've had other tasks keeping me occupied some of which included updating the electrics in the garage where the filter and stuff live which took me longer than anticipated (there's a pattern developing in my posts!). I did get half of the biocenosis baskets done, so ten out of my intended twenty, and I put these in the main pond to get them maturing. In order to keep the cat litter in place and discourage the fish from nosing around in the basket I put a good layer of decent sized gravel stones that I had been saving from a previous job on the house - ideal, I thought! So, in they all went to sit there until I get my ar$£ in gear and finish the filter pool where they'll live.

I did a water test last night to find my normally rock-steady pH level had gone from 7.5 on the colour chart to 9.0+! WTF . Initially I thought some brick dust may have found its way into the filter as I'd been drilling the wall above it for some additional power supply sockets - I'd been pretty careful but what else could it be? So, I did a partial water change (around 10%) immediately in the knowledge that I'd be doing another 10-15% today as part of my normal cleaning cycle. So today comes and I'm going through my usual routine; filter drained and flushed through, brushes jet-washed, pond floor pond-vac'd, water topping up etc etc. So having spent all morning doing the biz I expected at least a small improvement in the pH reading. Arggggh! No change at best and still showing 9.0+ on my chart!! That's when I wondered what else I had added to the pond recently. I know the biocenosis baskets, cat litter and aquabasis plus wouldn't affect the pH to that degree which is when I realised that the gravel chips I'd added to keep everything in place was friggin' LIMESTONE!! Doh!

So the baskets have been removed and I'll do another 10% WC now and 10-15% tomorrow. The fish don't seem overly perturbed although I did notice one or two last night flashing once or twice - they seem ok today. I'm conscious that too sudden a change is not good for them in either direction so I'll aim to get back to natural levels (pH7.5 where I live) over the next week and hope the fish are ok with that. If you guys have any other advice especially if my plan is flawed, I'd be happy to receive it. Hope everyone is well, it's been quiet on the forum so I thought I'd post just to let you know people are still looking in from time to time.

Regards, M

[Manky Sanke]

You have now seen first hand why I recommend sodium bicarbonate for adjusting KH and pH. It can't increase the pH out of the accepted range. Any form of calcium carbonate can increase the pH but it's a balancing act between how much is added and its tendency to rapidly raise the pH towards a value between 10 and 11.

You could try putting the baskets into the bottom half of one leg of a pair of stockings or tights, and tying the excess across the top of the basket or loosely around the plant stem if it's planted.

[Airlite]

Tights That's a brilliant idea. Yet again, thanks Syd. Mrs won't be too happy but needs must!!

[Airlite]

The tights idea has worked a treat! Baskets back in the pond and hopefully beginning to create some of that anoxic action in the near future. The pH level has also settled back to something approaching normal too, thank goodness! The colour chart on my test kit equates to 7.5 tonight but in order to be a little more accurate with pH and temperature measurements I've purchased a Hanna monitor to do the job from now on and I'm getting a factory calibrated reading of pH8.05 at 12.8C. More to do this weekend, I might even take a couple of pics and put them up here to illustrate the saga as it continues. Regards , M

[Airlite]

Hi fella's. Well, four months down the line and still the Anoxic Filter System (AFS) project is evolving (I know what you're thinking; Cathedrals have been built in less time)! However, despite the outwardly visible lack of progress, a small but significant step has been taken with the choice, purchase and installation of the RDF that I was procrastinating over for months. In the end, I went for the one that I'd discounted out of hand originally - the Oase ProfiClear Compact (gravity) on the basis that my pond is small at a smidge under 1500 gallons, I could just about get away with raising the water level by an inch in order to achieve the minimum level required in the drum without making any drastic adjustments to my garage floor (where the filter lives) and also the fact that I got a great deal on it from my local "koi dealer" (garden centre variety). So the old 2-chamber tank and associated gubbins has come out and the fancy box of tricks has gone in - at least as far as the pond is concerned at any rate. I've still got some work to do on the anoxic tank, not least of which is to decide how best to plumb it in as I've had to move stuff around a bit. If only I'd installed the drum before I'd built the tank!!

Prior to that excitement, all bar two of my planned 20 biocenosis baskets are made up and they've been maturing in the pond for weeks now. Manky's idea of securing the contents with the wife's smalls worked a treat and I'm guessing that they're already doing some good as I've had consistently low NH3, NO2 and NO3 readings since they've been in. Phosphates are still higher than I'd like but as the baskets aren't planted that's not surprising.

Next on the list is to position the 233 gallon/20xbasket AFS tank in it's final position in the garage somewhere where I can get to everything I need to get to and plumb it in. My cunning plan is to have the AFS tank perform a dual role; that of the anoxic filter (obviously) and also that of a quarantine tank as/when required. The idea is to have the ability to isolate the AFS tank from the main pond and have a separate/independent filter running on it when it's being used as a QT with the baskets removed and placed in the main pond (as they are currently) for the duration. In "normal" use the tank will be pump fed from the drum and, being raised about a foot or so above the main pond, the water will be piped back through the garage wall under its own weight. What could possibly go wrong?!

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