The mucky mystery of ponds sludge: The theory

Surface detritus could obscuring an unpalatable truth in the stygian depths.

Ponds sludge

The accumulation of dark slimy gunk in the bottom of your pond or filter system seems pretty evil stuff, and one of the most evil things about it can be its smell. In fact its presence and the way that it does smell is a pretty good gauge as to the health and welfare of the occupants of your pool or water garden. Not only that, once you get it out of the pond it could have its uses in the garden too.

The muck that accumulates in the filter can tell you a lot about the health of your pond.

Nasal knowledge

For those of you au fait with the aromas of pond bottoms and filter filth will know that there are some ponds that are little worse than a good honest workmans armpit sort of smell, or silage on a bright frosty winters morn; sweet and reassuring. Others are so pungent your head involuntarily flicks back at the slightest whiff and you explete Ewwphh! Your instincts do not deceive you. That really smelly stuff can be as harmful as it smells and it is certainly no good for any fish in the pool, nor is it any good for going straight onto the garden.

The material that you have possibly scooped up in your hand is more alive than any sci-fi alien gloop from outer space that is threatening to engulf the whole of New York State. This pool putrescence is in fact a mixture of millions of bacteria and the organic matter that sinks to the bottom of the pond (and or gets pumped up into the filter system). Those bacteria are busy digesting that organic matter, which in the process gets broken down to its constituent chemical parts. Originally it would have been plant material, dead algae or fish waste. Fish waste equals fish faeces and uneaten fish food. Both of these consist of large amounts of Hydrogen and Nitrogen linked in compounds, and the process of breaking them up into elements that are not toxic to the environment creates a heavy load on the eco-system of the pool environment. This means that a lot of bacteria and microbes need a lot of resources, and those resources are any available oxygen atoms. If oxygen is limited, you get the wrong bacteria down there attempting to deal with the problem and they tend to create a bit of a smell. It may not be as sentient as alien gloop but it does tell you something, one thing. If there is a faint hint of sulphur with a hefty ronk of ammonia or perhaps a waft of methane, then youve got a population of bad guys and that smell spells death for fish and everything that lives and breathes in ponds.

In the right situation they are not really bad guys. They are anaerobic bacteria that have their rightful place in the great tapestry of things, but they are best kept at the back end of the process of breaking up all this organic matter, that is, when most of the job is done. The guys you really want first at the Eat up All my Organic Waste Party are aerobic bacteria they need air (as in aero) to be there.

Why me?

If your pond stinks and your filter is foetid and you feel that you have been inflicted with the wrong sort of gate-crashers to your microbe ball, make sure:

* The filter system or the activity in the bottom of the pond has had time to get going before being overloaded with fish. It may need a biological starter.

* Treat any new water added to the pool as a top up with dechlorinator, often referred to as pool conditioner.

* If you add pool conditioner to the pool either do it with the water fall and filter system operating to ensure full circulation and mixing, or water a dilute mixture onto the surface from a watering can. N.B. Im doing neither here!

* Clean out small ponds regularly. Check filter systems every month and back-flush them on well-stocked pools. Have a major cleanout every six months. Do not use chlorinated water.

Large ponds may only need attention every four years at the most. It depends on the balance of fish and plants or fish and filtration.

* Ensure there are not too many fish and they are not overfed especially when the temperature of the water is dropping.

* Ensure the water is well oxygenated with a fountain, waterfall or venturi.