Been aware of this thread for a while and only recently been able to put my experiences down in writing and also show how my filter system was (and now is set-up) and the reason's behind me making the changes.
I had a "U" shaped which was 7ft up one side and then 7ft down the other side. Through the two 4" pipes into fluidized K1 and then into the matting chamber which was set up in a popular style.
Settlement:- You can see the water enters on the right of the picture from the bottom drain and goes around the top of the picture in the bend and through 2 x 4" pipes into the K1 chamber.
The matting chamber was laid out like the pond in Duncan's original scenario but with slight changes though again in that my "Bio" chamber was only 1.5ft wide. So each sheet of 2m x 1m matting i could cut into 4 sections. Meaning i had 6 full sheets in my filter (24 layers). All this was pulled through by 2 x aquamax 10,000's and through the heaters, UV etc back to the pond.
Matting Chamber:- In the picture below you can clearly see the lighter colour of the cheaper type of matting. I in fact added a few more layers (4 i think) after this picture was taken.
In the beginning i was very happy with the filter as it gave me crystal clear water - so much so i could see the screws on my bottom drain diffuser. I was adding weekly dose's of Clay (300g per week) and then Magic Powder (30g per week) and Super Clean C (30g per week) and i had very little maintenance and in fact 18months in when i "cleaned" the Bio chamber there was next to nothing in there.
The few koi i had in there were fine and I of course kept growing my koi collection in numbers and size.
This then led to my issues with the filter as the koi got bigger and i had added more fish, this put pressure on the system as food rates were well up. In the end every few weeks the matting would POP out of place and i'd end up with water tracking around it, Clarity would drop off, and instead of thinking (what's up?) i just pushed it back into place and get mad at the filter.
As is well documented on the web towards the end of 2008 i began looking at improving my water (RO etc) and this also meant looking at my filter system in an effort to make controlling TDS etc through ease of maintenance etc we came to to the conclusion that it could be improved.
I made the choice that i wanted a more maintencance free set up and i sorted me a set of Bakki Showers out to replace the matting. When i went to fit the Bakki i removed the matting and the pictures below are what i found. Now i think it was approx 6-8months since i previously "cleaned" the bio-side of the filters at this point although i couldn't be 100% sure on the exact timings.
Sure i hear the comments - "but it isn't black smelly sludge it looks light brown" - and to an extent it was but there was a "whiff" when i was removing the matting. I just personally don't see this kind of build up as beneficial to my filter or my koi and want it out of my system.
So i now run the same "U" shaped settlement - K1 Chamber and then over a 3 teir Bakki Shower. I do have 4 layers (1 x full 2m x 1m sheet cut into 4 pieces) of matting in my filter now to act as a polish and that's it. This is purely sacrificial and is pulled out and hosed off as part of my weekly filter cleaning.
Current filter set - up:- (Note the spraybar is missing as this pic was taken during the change over process)
Now i know i'm lucky in that i can run the showers inside and i negate many of the "downsides" of this filter system but the gains for me and the peace of mind is huge. A simpler / cleaner filter which means more time by the pond looking at the koi rather than cleaning filters.
Currently my matting is still sitting at the bottom of my garden in case i ever want to go back to matting. If i did i certainly would not be going back to the old way i had it set up - simply a polish / poop catcher. I'd be looking to do something different where i could get less trapped waste / products in between the sheets.
