More on Oxygen in Koi Ponds...

I sent this page out as an article but it is so important I have reproduced it here...

Many of you know Peter Waddington and Nigel Caddock -  and I am pleased to be able to reproduce some useful information from Nigel on aeration in particular...

Up until now, aeration is not a subject much considered by many Koi enthusiasts in South Africa...

Have we mentioned aeration?

by Nigel Caddock

www.koimag.com

Did you know if we put every word ever included in NI encouraging readers to put more air into their ponds the line would stretch to Japan not a lot of people know that!

Seriously, it will come as no surprise to regular readers to hear that if there is just one message above all others that we would like to be remembered for, its highlighting the role of dissolved oxygen in successful Koi keeping. There can be little debate that of all elements available to us, oxygen is not just the most effective but also the easiest to deploy and increase, and, it also has just about the shortest downside list on the planet!

Its worth revisiting some of the basics, perhaps the most important of which is that dissolved oxygen is the giver of all life in aquatic environments in general, and Koi ponds in particular. So why do you suppose that every year so many Koi keepers still get into trouble due to basic oxygen depletion?

As one of the most basic and simple elements its often taken for granted. Be honest. When was the last time you measured the O2 levels in your system? Sure you check ammonia, nitrite, pH but how often oxygen? Up to a few years ago there was a reasonable excuse simply because of the lack of availability of affordable and effective O2 test equipment. Tetra changed that ten years ago with the introduction of their ground breaking O2 test kit with their popular and familiar reagent format and since then a whole gaggle of manufacturers have piled in including more recently of a range of digital gizmos. In 2002 there is no reason or excuse not to check your DO.

Its also our view that of all water parameters dissolved oxygen in the most important single element, before ph, before ammonia and before nitrate!

There are of course many ways of adding oxygen to your system. Waterfalls, watercourses, venturis, turbo air domes, and of course air pumps. Oxygen is transferred into water via intimate interfacial contact of air and water molecules. As a rule of thumb the longer the contact time the better the O2 transfer. In general of all external constructions waterfalls are the most effective simply by virtue of the increased contact time they facilitate due to their nature. The downside to waterfalls and watercourses is that in addition to increased O2 transfer performance they also are effective at thermal transfer (William: Not really a massive problem in SA).

This is great in the summer when temperatures are high but less good in autumn and spring when large air temperature variations can occur, and if you operate your waterfalls you could either get a big gas or electric bill for your heating or risk inducing large temperature fluctuations. Best advice is make sure you build in waterfall/watercourse by pass units so you can return water either via the waterfall or an in pond return like a TPR. This additional operational flexibility is good design as well as offering a highly practical solution.

Chemical Stability

One of the less understood benefits of high levels of DO is that toxic elements, notably ammonia, are less toxic when DO levels are elevated and vice versa. Consider a scenario if for any reason you get an ammonia spike in the summer when temperatures are high and its a sultry day, its not hard to understand how we can end up in serious trouble in a relatively short period of time. When your Koi are gasping at the surface consider again if the price of a spare air pump is really too high?

Temperature

To maintain appropriate levels of oxygen in your system its vital to understand the relationship between water temperature and the waters ability to absorb and retain oxygen. In basic terms the higher the temperature the more oxygen required to reach saturation. To put it even more simply enough aeration at 55˚F/12˚C may not be enough at 80˚F/25˚C.

What is it (DO) measured in?

Often numbers quoted in relation to acceptable levels of oxygen have been referred to in parts per million (ppm) 6 being the magic number. Problem is that all the published data and recommendations refer to salmon trout or other farmed fish. Its our unequivocal contention that these have little to do with Koi. With the help of Jasper Kuijper and the unique EA test facility, in time we hope to generate better data specific to Koi. In the meantime we believe that empirical numbers developed with experience and over many years to be more useful than definitive data relating to trout and salmon. The numbers are offered specifically in this context and we make no claims that they are in any way definitive.

Dissolved oxygen is appropriately expressed in milligrams per millilitre. The table below indicates the vital relationship between DO saturation and water temperature. This relationship is defining and needs to be carefully considered at all times. To give you an example DO saturation at a water temperature of 5˚C is 12.8mg per litre and when the temperature is 25˚C saturation is just 8.4mg.

(William: Saturation means maximum - i.e. the maximum amount of oxygen that can be dissolved in water, no matter how much extra air you blow through the water, the maximum oxygen level is fixed and determined by the water temperature.

So not only is it more difficult for warmer water to absorb oxygen, but it dissipates faster and more effectively also. Thats the basic reason that summer ponds are more susceptible to oxygen depletion. Throw into the mix atmospheric factors, i.e. humid sultry weather which compounds the pressure on the vital DO and what you have is a problem waiting to turn into a disaster (William: HEAR HEAR!). If you have relatively high stocking levels you just lit the blue touch paper!! Consider too that at elevated temperatures Koi respiration rates increase with activity and oxygen demand from your vital filter bacteria who are also in turbo mode, also increases significantly so the danger zone increases still further.

As with all things in Koi, balance is the key. Its simply the experience of many Koi Keepers that providing aeration avoids the potential problems we have identified. As another of our key themes is prevention and in this context prevention = aeration, its not rocket science to work out what the solution might be.

An additional point to consider is that most medications also absorb prodigious levels of oxygen during their reactions. If you need to treat your pond its always a good idea to compensate by adding extra air but when temperatures are high take special care. In fact as a matter of good practice its a good idea always to add extra aeration when you medicate your pond and its always good practice to have a spare air pump for this application.

How much air?

Aeration is about control. By deploying air pumps to make sure that DO levels are sufficient, you take control of one of the primary requirements of your Koi system, as a basic principle we believe this to be a sound principle. As far as we are aware no one has previously put numbers to the requirement of air. In good NI tradition we figured its time someone did so we have! The numbers in the table necessarily are indicative as they need to accommodate an almost infinite number of variables: stocking rate, feeding rate, filter size, filter efficiency, maintenance, etc, etc etc.

The problem is that it is virtually impossible to fulfill all these in a model that could accommodate all the variables. Our numbers therefore make some assumptions and judgements and rely on experience. We recognise this empirical approach is not perfect by any means. However by the same token it also deploys our combined experiences to offer what we believe to be a sensible guide.

In general terms, 40lpm per 1000 is a good rule of thumb (William: this is flowrate). We fettled the numbers simply because of some general principles, for example ponds up to 9 000 gallons tend to be stocked heavier than ponds of say 20,000 gallons. In addition bigger ponds tend to have bigger surface areas which generally offer better DO exchange opportunities than smaller ponds. These comments are offered to provide only a context for the numbers not to justify or qualify them, and we would again reiterate their entirely indicative nature.

Where to put the air?

The simple answer is it doesn't really matter. There are of course numerous options: turbo air domes in-pond diffusers or in the filters, our experience is simply that the only relevant number is the level of system DO. While filter systems consume large quantities of air it makes sense to deploy air in the filters, air bubbles relax Koi so turbo air domes are great for that. Add their ability to mix and the low pressure regions they create which in turn assist bottom drain function it makes sense to include them.

One development that has emerged in the great what size air line to use to feed air domes debate is solved with a TOP TIP once again Sean Hunter of Reflections fame came up with the answer neither! What the intrepid Mr Hunter did was feed the dome with a 1 pressure pipe with connectors at each end and then pressurise the 1 pipe with air! Absolutely brilliant. Less back pressure on the air pump, enhanced performance of the dome and no crappy air line to kink, get blocked, become detached or perish! Best of all like all great solutions absolutely simple.

When putting air into filter chambers we need to consider that air also creates pressure. For example by placing them in transfer ports which is good in one way because all the air has to flow past it, there is a risk that the air creates enhanced back pressure and a mini air lift effect, this in turn results in the water flowing from filter to filter being impeded and water levels in downstream chambers can get too low and even starve end chambers. No big deal but it needs to be considered. In contemporary systems much of this guesswork has been designed out.

What to use?

In the early 1990s this was an easy question to answer. Hi Blows were the only choice. Made in Japan imported by Hagen and simply unchallenged. Then the industry decided to turn air pumps into the number 1 discount loss leader in the business. All manner of cheapo repros emerged, good news on the surface as prices fell, but the problem was in an effort to compete, manufacturers down specified components to the degree where reliability which was never previously an issue became a problem of almost epidemic proportions.

Along came Secoh and delivered a great 40. The problem was their bigger models never met the same performance of the 40s and specifically, in common with numerous makes, the diaphragms emitted dust which blocked air stones and even multi port outlets. This in turn can increase back pressure and precipitated premature failure by default. Add to this a disturbing propensity for air pump makers to specify operating depths that effectively made them inappropriate for Koi ponds. It never did stop them selling them to Koi keepers though, as we pointed out. Nevertheless they were very disappointing. Thats why you wont have seen ads or editorials for several years recommending air pumps.

Since the mid 1990s many manufacturers have emerged and delivered a wide range of air pumps in a wide price disparity, so how do you choose which air pump to buy? We believe there are several key factors. First, experience and second, market endurance. Most dealers and Koi Keepers know very well which units are good and which are not, and even more important which are a disaster! Best advice is talk to your local Koi professional and get his recommendation, then talk to as many Koi people whose opinion you respect, and see what they think and what they use. After youve done all that consider all those factors and then make your choice.

Performance data can also be useful but make sure you are comparing like with like. Manufacturers are masters at presenting technical data that makes and shows their products in the best possible light, no problem with that as long as the playing field is flat or at least flatish!! In an effort to clarify this we have some numbers for you to consider.

Performance curves in relation to air and water pump performance are standard tools of the trade to most professionals, for we hobbyists they are normally just utterly confusing. In an effort to blow the gaff on this mystique we thought we would present one to you and discuss it in detail. There is no doubt that by far the most popular size of air pump is still the 40 litre per minute unit. But what does the data really mean to us as Koi Keepers and how can this information help us make a good air pump buying decision?

First its important to consider that there are several key elements that contribute to the performance of an air pump.

1. Output expressed in litres of air per minute

2.  Pressure usually expressed in kg/cm2.

3.  The other key factor is amount of power used.

The problem is these terms mean little to most Koi people so we thought we would try and help make it more understandable. The output numbers are not so complicated as most understand litres per minute Hi Blow 40, Secoh 40 Koi Air 40 etc, all blow 40 litres of air per minute.

The pressure and power numbers are however equally compelling. For example its not much use in deploying a 40lpm to drive the air domes in your 2 metre pond when chosen units cannot cope with the pressure (pond depth) and actually only dribbles a pathetic 5 lpm at 2m depth! This is where paying attention to the performance curves of air pumps and water pumps is vital.

If we take the H/K Airpump performance curve as an example. The left hand vertical column indicates the output of the air pump expressed in litres per minute. The horizontal line of the graph shows pressure which is expressed in kg/cm2. This can easily be converted into pond depth and this makes it much more easy to understand (for Koi Keepers to understand, we added the depth numbers as well), but here they are:

0.1kg/cm2 = 1 metre pond depth

0.2kg/cm2 = 2 metres pond depth

0.3kg/cm2 = 3 metres pond depth

0.4kg/cm2 = 4 metres pond depth

0.5kg/cm2 = 5 metres pond depth

It is often the case that performance curves are qualified and that output number are determined at normal pressure. In the H/K Airpump case normal pressure is 0.13kg/cm2 which simply means that at 1.3metres the H/K Airpump is guaranteed to output 40 litres of air per minute. If however you check the performance curve you can see that in fact you don't get 40 lpm you actually get 56!

When we interrogated the manufacturers they confirmed that in fact in their tests the numbers exceeded 60 litres per minute! This is a big deal for us as Koi keepers because it actually means we get a 60lpm model for the price of a 40!!

This can also work in reverse so thats why it is important to check the curves and understand them. To get back to the H/K Airpumpcurve, what it also tells us is that at zero pressure it actually outputs more than 80lpm! It also shows us that at 4.4 metres the pressure is such that the pump will produce no air at all! The profile of these curves are also vital when selecting which unit is best for you, and its important to appreciate that this can be different for each individual application within your system. Ensuring you get the right unit for your application  -this is another reason for you to invest a little time understanding how the curves work and how to interpret them, and it can save you a lot because if you deploy a unit incorrectly chances are it wont perform as you hope and it may even compromise its performance and shorten its operational life.

There is another useful rule of thumb that relates to power consumption. In general a good per-forming air pump will deliver 1 lpm for 0.8watt. So for a 40 lpm units the power consumption number needs to be around 32 watts.

Maintenance is Vital

Like all mechanical devices, in order to get the best out of your air pumps you need to maintain both them and the systems they work within. Specifically replacing diaphragms (for units that have them and some don't) and air stones which are especially critical because if/as they block they increase the back pressure on the pump which in turn can compromise performance and life expectancy. Don't just throw in air stones and forget them, they will block and need regular cleaning and periodic replacement. Failure in this area and to exceed operating parameters specified by manufacturers will invalidate product warranties.

The point of all this is to illustrate that when it comes to selecting air pumps for your Koi system you need not just consider the capital cost of the unit but a whole range of other factors that together represent the Total Cost of Ownership.

The TCO is the real overall cost associated with owning and using an air pump. This includes purchase price, running cost, maintenance cost and the hidden costs of any failure!

Consider a unit that's less expensive to buy but that fails or loses power at a critical time, how much is that worth? Consider a badly designed first generation air pump that's relatively inexpensive to buy but uses three times as much energy to deliver the same output? How long before the extra capital cost of a more efficient unit eats up the extra original capital cost differential and then actually starts paying for itself because of power savings!

When it comes to air pumps, reliability and performance have to be major considerations. Most manufacturers offer a one year warranty, so if someone offers two years then that must say something about their confidence in their products? By the same token if a unit consistently demonstrates its total lack of reliability, the market soon marginalises it.

The notion that air pumps are the ultimate loss leader in the Koi business, is outdated given the degree of investment some manufacturers have invested in developing their products. In 2002 and beyond, demands from users have never been higher so its good to see some makers rising to this challenge and actually understating the overall performance of the equipment rather than the usual barrage of brash unsustainable hype we are depressingly used to.

Talk is cheap, best advice is to check them all out and then use your common sense and experience to make the right smart choice for you!

That's it! (William: Eventually! Buy it's been worth it!)

Regards

Nigel

As I said, long but now you know everything you need to about air pumps and WHY they are so important, and more so in South Africa with our warm climate and often our high altitudes (which further reduces dissolved oxygen levels). Consider an H/K air pump (a shameless product plug - frankly I care less about WHAT air pump you use as long as you use them and you have enough air for your pond) and mail me with any questions you may have - I'll try and answer them as best I can.