Having spoken to the manufacturer regarding the Zeolite stone, the replies given did not exactly fill me with confidence. The claims were that it could absorb its own weight of ammonia before becoming fully charged, after this it was ineffective and would need cleaning.

I followed the advice given by the manufacturer to weigh and mark random pieces after they had first been soaked in fresh tap water for 24 hours. This done I placed a tray of it with the random pieces clearly marked in the first bio stage of the main pond filter.

I kept weighing these random pieces at monthly intervals and only after 10 months did I get a slight (5%) increase in weight. I had already given usage instructions by way of a leaflet attached to each sack that explained all this and the ways of re-charging the stones when required.

The re-charging could be done overnight by submerging the fully charged stone in a separate container with enough fresh water to cover it and then adding salt at the rate of one kilo per litre – as you may guess, this was impossible to dissolve!

Later I heard comments from others warning them never to allow salt into a pond that contained Zeolite as the salt would release the ammonia and poison all the Koi???

It’s quite amazing how some simple instructions can be twisted.

Moving on to the Wakishimizu unit, originally I set up a separate 10 ton Koi pond in the treatment area of the building and connected it to a side feed as instructed. It was a circular plastic upward-flow unit around 18” in diameter and around four feet tall. This was not a pressurised unit as were the larger ones, and simply had a lid that could be removed when required.

The manufacturer said there was two completely separate stages to these units, the first was the mechanical stage and the other was the biological stage.

On first inspection of the mechanical stage, the media was identical to the media contained in the bead filters of today, although I wasn’t to realise this until many years later.

The unit came with its own water pump, pressure gauge and various 2” control valves that were all fully automated. A simple perforated tray above and below this media prevented the beads escaping the box either into the biological stage or down into the waste lines.

When the pressure gauge indicated that the beads required cleaning, in stepped the automation. The water pump was switched off, a valve closed the return line, another opened the waste line and the water pump turned back on to backwash the beads. Once the pressure gauge indicated that the cleaning had been done, it automatically turned back to normal running.

In those days this was a rare delight to watch.

However, it was the biological stage that confused me the most. To describe it, this was a sheet cut to size of a clear plastic material that represented an open honeycomb when viewed from above and below. The depth of the material was around 9” and the plastic that formed the honeycomb was paper thin, of course it weighed hardly anything.

I couldn’t possibly grasp back then how water could be ‘filtered’ simply by passing it through a series of open holes?

The Wakishimizu ran well for a few months before the automation failed, but the high prices of these units, plus shipping costs would make these units very difficult to sell – yet another project abandoned.

In spring 1984 I discovered another biological media that also ‘filtered’ water through a series of open square spaces after Toshio Sakai finally informed me of his experiments with a material made to allow drainage of road surfaces when placed beneath these final surfaces.

He had formed the flat sheets into upward-flow cartridge blocks that were tailored to dimensions of his filter chambers and, after removing all the stones and gravel inside, he replaced them with these cartridge blocks.

In comparison to the heavy stone media these cartridge blocks were extremely lightweight and lasted indefinitely when submerged in water.

Toshio insisted that maximum performance of these open blocks could be achieved by adding heavy aeration below them.

I admit I had problems understanding his system, but after witnessing the water conditions these blocks produced on his ponds I had no hesitation in ordering a sea container to be filled with sheets of what I later christened as ‘Japanese Filter Mat’, various sizes of ‘Hi-Blow’ high-output air pumps and a new mechanical media being given rave reviews in Japan, namely the FOK filter brush.

These three items finally arrived for the first time in the UK in autumn 1984. Bearing in mind, no one in the UK had ever seen or heard of any of these items before (the only air pumps available were the ones used in aquaria) you can imagine how difficult it was for me to advertise, market and sell them.

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