Very soon after we also learned that pond plants in a man-made water-retaining structure did much more to damage the water make-up – rather than to simply appear to be ‘visibly natural’.

I can’t recall exactly when I first heard the term ‘pond filter’ mentioned – but it did seem to make some sense to me. After all, the term ‘pond filter’ must also mean ‘pond clarity’ and it would be nice to see our pets in crystal-clear water just for a change?

The popular filter for aquarium keepers back then was known as ‘the under gravel filter’ where a drilled plastic plate the size of the aquarium base was placed on the base and covered by a 1” layer of gravel. An air pump was connected to the plastic base that drew water downwards through the gravel and ‘air-lifted’ the water to the surface of the tank.

This was soon emulated by the keener Koi keepers of the day, by lifting out the pond liner and excavating a rectangular 12” deep, flat area, usually in the shallowest area of the pond, before replacing the liner.

Instead of a plastic plate, a network of 1.5” drainage pipes that led to a common manifold replaced this. The pipe had ¼” holes drilled straight through at random intervals (pure guesswork) and this network was buried under a 6” depth of washed pea gravel. A submersible water pump replaced the air pump and after connecting it to the manifold, this drew pond water down through the gravel bed and pumped the water back to the pond.

This seemed to be a perfect way of cleaning the water and also restoring good clarity, and it did just that!

Alas it only did ‘just that’ for a few months before the water pump started to slow down and then continued to slow down. Many water pumps burned out as a direct result of total mechanical blockage in the entire gravel bed. Immediately after this was detected it was a matter of great urgency to remove all the Koi from the pond before ‘grey water’ and severe anaerobic conditions followed.

Then came the need to take all the gravel out and clean it thoroughly before blasting the insides of the pipelines, replacing the gravel and starting the system up once more.

Later some well-meaning Koi person suggested the reason for this blockage could be because finer mechanical particles could be passing through the pump and back into the pond water. He suggested a swimming pool sand filter could be fitted after the pump and this would take in these fine particles and thus ‘polish’ the water?

It sounded logical to many of us as the thought of constantly cleaning bucket-loads of filthy gravel wasn’t the kind of ‘happy Koi keeping’ we’d expected.

The 18” model of the Lacron sand filter looked puny to most of us, and the 24” model didn’t exactly inspire confidence either. However the 30” diameter giant looked to be the perfect choice for the few dedicated Koi keepers around the country.

We bought them and fitted them only to discover our submersible pumps simply were not nearly man enough and only produced a trickle back to the pond. After a few disgruntled phone calls to Lacron, they told us the reason it was happening is that we also needed to replace our submersibles with their mighty external range of ITT Marlow pressure pumps!

Of course we all shelled out more loot and ordered these external monsters. Pretty soon we had perfect filtration for a few months where we congratulated each other warmly on our very wise choice of filters.

That was, until the first quarterly electricity bill landed!

(It was quite easy to wriggle out of that one for me by complaining bitterly to my wife as to the ridiculous high running cost of her latest clothes dryer.)

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