Danger Of Organic Wastes Build Up In Koi Ponds

The more and more I see of Koi ponds in South Africa, the more I wonder at the sheer dedication of these often fanatical people that maintain these ponds in their often pristine condition. It looks like a lot of work to me.

And make no mistake, it is! And that started me thinking about why there is so much maintenance that has to take place in a Koi pond, as say compared to a home aquarium that in many cases only needs a muck out every month or so. Mine, in fact is lucky to get one every 3 months! Yet the fish live on and on in perfect health.

The answer of course to Koi pond maintenance lies in the Koi themselves. Because they're carp, and carp are water pigs, Koi eat a lot. Which means that they produce a substantial amount of waste, both dissolved inorganics (ammonia) and solid organics, the stuff that you get to see and have to muck out all too often. The more they eat, the more they produce, the more cleaning has to take place. The warmer the water, the hungrier the Koi and South Africa with its near ideal Koi climate, well, you get the picture.

But why remove the solid wastes?

Solid wastes are largely composed of organic matter. There is some fibre, ash and other inert rubbish in there too that comes as part of the Koi's food that it simply cannot digest and which passes straight through it's digestive tract into the koi pond water. But the nasty stuff is the organic component of this waste.

Left alone, this organic waste is an ideal food source for heterotrophic bacteria. These fast growing oxygen demanding bacteria will happily munch on this waste till their tummies are full and they split off to create a thousand more hungry bacteria that then engage in the same process. Eventually, the theory is that all the 'food' will be gone and the bacteria will naturally expire of starvation.

This doesn't sound so bad does it? But in truth in the process of eating all this 'food', the heterotrophs are doing three things. They are producing a whole range of by products from the decomposition of the 'food' into energy of which some are not great to have dissolved in a Koi pond's water system. Hydrogen sulphide for instance is nasty. They are however also producing ammonia - the very inorganic substance that we're trying to be rid of! And lastly these bacteria are consuming oxygen at a prodigious rate.

Imagine a warm summers day. Imagine a pond of happy Koi swimming around. They look magnificent and they're feeding well. They've grown to a massive 60cm each and now when they feed, they REALLY feed. Lots of waste is produced, but that doesn't matter because your bio filter is monstrously big - it IS monstrously big isn't it?? - and you know that your system can handle any waste load.

Or can it? A bio filter removes INORGANIC wastes, the non solid stuff. It's dissolved - you can't see it. Your mechanical filter has to take care of the solid visible stuff. Sand filters are one nightmarish way (I have an upcoming article dedicated to this topic alone), vortexes a slightly better way and the Answer the best way of achieving this removal.

The problem with vortexes is that they still let some suspended solids through into the bio filter stage. Best guess estimate put this figure at as much as 70% (!) in some cases. That's an horrific amount of solid organics landing up in your bio filter where the unwanted heterotrophic bacteria can then compete with our much wanted nitrifying bacteria for valuable oxygen and valuable living space (bio media is the equivalent of urban real estate for bacteria). Heterotrophs are a much faster growing spectrum of bacteria, so they can quickly take over as much space in the biofilter as their food source (solid organics) and oxygen levels will allow.

And then these invasive bacteria add insult to injury by adding to the ammonia levels in the bio filter!

Many of you will have had ponds for many years without noticing these kind of problems. This is because the organic load is not sufficient to entirely overload your bio filter system, since we have monstrously big filters right?

May you never experience bio filter overload, God and stocking levels willing. But when it comes to the hobby of Koi keeping if it can go wrong, eventually sooner or later you and your filter system will be tested and you are found wanting there is very little you can do about it in time to save your Koi. Such problems are quick, ruthless and devastating.

In the cases where ponds move from year to year with no problems, the bio filter is usually adequate. By adequate I mean that it does the job well enough to keep Koi alive. Koi are tough fish and it takes a lot to bump them off. That said we are noticing a trend of increasing sensitivity by the more highly bred specimens - similar to the dog world in which breeders of highly specialised pedigrees are starting to introduce new bloodlines into their dogs to try and overcome temperament and physical problems that are becoming more and more prevalent (the German shepherd being bred with the Belgian shepherd (Malinois) in order to improve drive and temperament being an example)

If you have solids waste in your fish and you want to get rid of it click through to this Viresco site

Article by William Kelly