Aeration… how much and where to put it.
There aren’t many serious Koi keepers who don’t understand and address the importance of providing our Koi with sufficient Oxygen. The reason being most of them will have first hand knowledge of what happens when there’s not enough…bad things happen and Koi die!
The relationship between the level of oxygen in a Koi pond and the water temperature is technically well understood. However, what’s less so is the ability of the pond water to retain and absorb Oxygen. Here’s a simple table to illustrate the point:
Water Temperature Oxygen Saturation mg/litre (ppm)* 10˚C 11.3, 15˚C 10.2, 20˚C 9.2, 25˚C 8.6
*Note: Mg/L and PPM (parts per million) are the same, just a hangover from the metric – imperial years!
What this means in practical terms is that to maintain the same level of O2 saturation at 20˚C that you have at 10˚C requires 30% more aeration.
If, in your wildest dreams, pond temperatures ever actually hit 25˚C the number increases above that, and when we consider the waters further reduced ability to absorb and retain O2, means this is a challenge we really need to be aware of, and up to. But there’s another red flag issue thats also much misunderstood…the rate that O2 actually reduces and depletes in a Koi system, when the power and air is off!
It’s not unreasonable to conclude that if your pond is at or around O2 saturation the accumulated oxygen in your pond will sustain your Koi for a period in the event of say a power failure, but the real question is how long is that period? The answer might be both surprising, and a bit scary.
While of course this issue is more critical at higher temperatures, the principle applies at all temperatures, so lets take a summer high pond temperature of 20˚C as our example point. If your pond is at or around O2 saturation and you have a power cut, so all the circulation and air pumps stop, with a O2 level of 8mg/l within 5 minutes that number will have dropped to 7, and within 30 mins will be below 6mg/l. That’s already too low for comfort and the reality of this data is that within the hour your system – Koi and filtration systems, will be in serious jeopardy! If you live in Denver Colorado or Johannesburg (at elevated heights above sea level) increased atmospheric pressure render the numbers are even worse, and the reality is you need more aeration and have less time to fix any failures!
The role of circulation and aeration pumps are also irrevocably linked to O2 levels in Koi systems. so it’s not enough just to effectively aerate your pond but its equally important to effectively distribute oxygen throughout the body of your pond. This is achieved using filtration circulating pumps but if, for any reason, your air pumps continue but circulators fail expect O2 levels to fall between 10%-20% within 30 minutes!
Although this failure scenario is less critical in terms of oxygen, its obviously extremely critical in terms of maintaining nitrifying bacteria in your filters, so clearly does require immediate remedial action.
This conveniently brings us to another misunderstanding we’d like to address, and thats the misnomer that filters especially moving beds bakki showers and trickle filters actually add oxygen to our systems. They don’t, in fact they are nett users of O2 – QED. If you don’t believe us do what we did, get a O2 metre and measure the levels on filter outlets, in fact take measurements throughout your system the results will be fascinating.
As we’ve learned in the previous section, nitrification is two stage dynamic chemical process that requires Oxygen and lots of it. If you test the O2 level of your pond water exiting your filter system, it will be less than the pond water entering it. In addition to following manufacturers guidelines for the amount of oxygen needed to effectively oxygenate your filters, these numbers should be considered as well as the necessary aeration in your actual pond. Of course this will vary from pond to pond depending on temperature, stock and feeding levels, but the key point is aerating your filter isn’t enough and we have some simple advice for you
…when your pond is above 10˚C for every 5000 litres Deploy 40 lph supplementary aeration 24/7, 365 days a year! PS: Make sure you always have a spare air pump available for WHEN one of your fails!
In this day and age there are some great diffuser options from ceramic air stones and diffusers through air curtains and although it may be a bit unfashionable, still our absolute favourite the good old aerated bottom drain!
When it comes to Oxygen and our Koi the reality is, based on all our experience, that the two are inseparable. In addition its also important to make sure you have some form of back up plan in the event of power failures. While our USA pals are much used to making such preparations its clear that UK hobbyists would benefit from addressing this thorny issue too, especially given the revelation of just how fast ponds loose their O2 when the power fails. A whole range of inexpensive generators are now available and it might be the best couple of hundred quid you ever spent!
Finally, it’s not just our experience that renders us 100% guilty of being obsessed by aeration, and not only do we make absolutely no apologies for our fixation, if and when you are fortunate enough to visit Japan and some of the legendary breeders, we challenge you to find a single Koi breeders premises where every single pond doesn’t look like a jacuzzi! Its not a matter of if its “good enough for them its good enough for us”, although in this case it pretty much is to be frank, but all our combined experience, and that of all the UK’s leading Koi professionals, and finally as we’ve demonstrated the science also backs up the contentions.
