This 4,500-gallon Koi pond system is waiting for some final landscaping touches to be completed later this month.

The pond itself has a single centrally placed diffuser bottom drain and the construction is from concrete block plus render and finally waterproofed with glass fibre. The pond has one surface skimmer powered by a water pump that pushes water through a 110w U/V unit and an electric heater before being returned to the pond some 70cms below water level.

The filtration system is a gravity-fed Eric FOUR unit connected to the bottom drain via 4” tube and at the other end of the unit a water pump and a 2” flap valve have been installed before the water is taken directly back to the pond also to enter some 70cms below water level.

This shows the system just after installation and the lady who owns it.

The lady owner lives in a beautiful part of the world as far as climate and scenery are concerned, namely Montpelier in the south of France. However, in terms of Koi dealers, Koi pond installers and Koi dry goods suppliers in her surrounding area there are none at all!

Everything that was needed for the pond and the vast majority of the labour was supplied from the UK.

To further complicate matters, there are very few Koi keepers even remotely near to her and this is her very first experience of Koi keeping so her only real information and assistance comes from UK Koi forums, thankfully she speaks perfect English being born in the USA.

It really is just about the most perfect small Koi pond system one can imagine, being very simple to maintain and very economical in terms of running costs.

The system was started up properly for the very first time some three months ago after first being to the greater part filled with very green water from a large, portable, above-ground swimming pool where her Koi had been kept for over one year without any filtration except for a daily 10% water change.

The ambient water temperatures in winter there are very mild but the summer temperatures can be extremely high and the water was the darkest green imaginable when it was used to fill 75% of her new pond. The remainder of the water was added from the mains and this is how it looked a few days after start up.

For the first week or so of running the water clarity began to show a daily improvement and with the daily dumps of the filter together with a constant trickle of mains water to replace it I was confident that the system would soon be perfectly clear.

Alas, that wasn’t to be because no sooner had it reached a point where the bottom drain could be seen, back came the green water with a vengeance and has remained like that ever since which is not the best of advertisements for my filter systems!

The standard water readings were always acceptable and the Koi themselves were always feeding like vultures!

The hours of intense sunshine and high water temperatures were held responsible for this but I wasn’t convinced, surely a 110w Pro-Clear U/V system could cope with that volume of water easily?

And what of other larger Eric systems in Malaysia with equally high temperatures where the water was always crystal clear?

So the next step was to increase the U/V capacity and a new underwater one is already there waiting to be fitted.

On late Friday evening 29/06/12, the lady rang to say she had a feeling something was wrong with the water pump driving her filter unit. The two water pumps used on the system are identical and whilst the skimmer pump was warm and vibrating to the touch, the filter pump was not warm and not vibrating.

I asked her to switch off the filter pump and contact an emergency electrician to check it out. The electrician came the following morning and confirmed that the pump had burned out but had no idea as to when this actually took place.

Yes, hindsight would have been a good idea to have had a replacement pump there which meant the burned-out one could have been removed via the union valves and the new one connected up and running within minutes.

Alas, there was no spare and the chances of finding one locally were not even worth considering but something had to be done to get water through the filter!

After some telephone instructions from me, the lady removed the brush box and all the six cartridge blocks after dumping the entire filter to waste. She then hosed down the insides of the box and then stared to hose down the brush box and cartridge blocks but rang back to say they were almost as clean as a whistle?

Thankfully I had been to the pond in the early days and knew there was a large submersible pump and hose in her garage.

I asked her to replace the brush box and the first five cartridge blocks only and in the space left by the sixth block I asked her to place the submersible pump centrally on the base and then cut the hose just long enough to reach the pond and then securing it with a stone before switching it on.

By early Saturday afternoon 30/06/12 this is how the filter was ‘running’ but at least it was running.

At least this would give me time to order replacement pumps and arrange to have them driven down and fitted by Ian Miles who had installed the system himself some three months ago.

Then followed the strangest phone call later that same evening from the lady to tell me that her pond water was clearing at an alarming rate!

I asked if she could be imagining things but she said she’d take shots the following morning and send them.

These are the shots taken only 18 hours after the makeshift Eric had been switched on.

Not crystal-clear by any means but I think that’s the first time I’d been able to see the bottom drain?

Things just didn’t add up to me?

Not only was the unit operating with minus one cartridge block but the circular end baffle that produces the vital forward moving block of water was also not working at all!

By then I’d asked her to place the submersible on a 6” block in order to draw water more centrally and later asked her to switch off the submersible and carry out a full dump of the filter.

An email came back to ask – ‘Should I always switch the pump off before dumping the unit and why does my filter overflow slightly after filling the box’?

WHAT?

I rang back immediately and asked if she had ever switched the water pump off before dumping the filter and then asked if she’d ever seen the filter slightly overflow when re-filling on other occasions?

The answer to both was ‘NO’!

If the water pump had not been switched off when dumping the filter then this could have meant the pump burned out months ago and if the filter didn’t slightly overflow on re-fill then it was guaranteed that water levels in both pond and filter were identical!

In short, there had been no mechanical and biological filtration on the pond for well over 10 weeks!

The only thing keeping the Koi in good condition for all this time had been a dump of stagnant water from the Eric box and the constant trickle to replace it.

Here are shots taken on the morning of 02/07/12 only some 40 hours after the ‘severely crippled’ Eric unit had been in operation.

And these were taken in bright sunlight with many reflections obscuring the actual clarity of the water.

As to water quality readings taken at the same time –

pH – 7.2

Ammonia – 0

Nitrite – 0

Which now raises other questions with me, namely the 110w Pro-Clear U/V has been working from the skimmer pump for the duration and yet the water has always been very green?

How is it that a seemingly brand new and thus perfectly immature filter system can change all this almost instantly?

Here are the latest shots taken at 7.00pm today 02/07/12 and water quality readings remain to be exactly the same?

No green water but water that’s getting clearer with each passing hour.

Throughout all of this the Koi in the system have not noticed a thing and in a few days replacement pumps and spare pumps will be delivered so all’s well that ends well and lessons have been learned.

Now as to ‘why’ this entire event has come and gone without any serious problems and even Koi losses being suffered, the only explanation I can come up with is this.

Despite the fact that owner had no idea that the filtration system was not in operation, because of the high temperatures and intense sunlight she religiously dumped her filter to waste daily and on some days she dumped it twice.

After the dumping had been carried out, the unit was filled with a new supply of ammonia-laden water from the pond and although it never moves forward and never returns to the pond, it stands there amongst the filter surfaces whilst the turbulence continues and so the bio film also continues to enable the nitrification process to take place on the media surfaces.

Pretty soon all this water will be dumped to waste and a new supply of ammonia-laden water (food) will enter from the pond and thus the process will continue.

I believe that when the submersible pump was started up for the first time it was also taking water from a fully mature filter system – hence the stable water quality readings experienced!

In Koi ponds, from time to time things must go wrong as outlined here, but unless we discover why they went wrong and then take the correct ways of putting them right then the problem will always remain to be an unsolved mystery.

Peter Waddington 02/07/12