DIY Bakki Shower The Koi Pond Project(s)
Previous pond at previous home.
Pond Mark Two "Koi Pond and Filter Mk 2 with DIY Bakki Shower"
February 2009. With all the fish gone (14 dead and 5 given away - couldn't risk cross infection) I began by nuking the whole system, including the filter, with Chlorine.
Then all the water was drained and the pond inspected closely for the first time in 16 years.
The G4 surface was no longer jet black, some of it had flaked off, but the
black surface resin over the glass fibre was fine.
Having scrubbed off the dead algae there was also a large amount of limescale
deposits – not surprising in our very hard water area.
The only major job was to reset the slabs around the top of the pond, because years of frost had loosened them.
The major job was to be in the filter.
The filter was fine for 1993, but things have moved on and the size of fish
I crave for has grown.
An empty pond and filter gave me a unique opportunity to plan a major upgrade.
This is what I did..
The concrete and glass
fibre structure was fine apart from resin cracking in the large 1 x
1 metre chamber.
I removed the resin and recoated with clear G4 (better penetrating than black,
cheaper and this bit won’t be seen).
Once the basic original structure was checked out and patched up came the planning
for the new filter.
Filter Planning:
After much research I drew up these schematic diagrams of the new system:
The pond is the Vortex chamber. The photos in the previous "chapter" show how
the rectangular top blends to a curved and oval hopper shape.
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Image to Enlarge
The unique "suction" bottom drain is retained as this has never blocked and has always pulled out all debris.
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Image to Enlarge
The stage shown above has remained unchanged apart from the use of Kaldnes K3 and extra air stones.
The flow from the pond can be varied infinitely from each inlet or blocked to allow independent filter cycling.
Click any Image to Enlarge: 
The DIY Bakki Shower.
I know that Alphagrog
isn’t the best media, but I had loads and decided to use it.
I decided I wanted my “stack” to be enclosed, to avoid splash, noise and Winter
chilling.
I wanted to design it so that there would be good through ventilation.
I can’t be sure if it’s a Bakki Shower or a Trickle Filter, but given the high
flow rate and air supply I’ll go for the former.
The media trays were stacking crates which took some finding. Getting just the right size, and stacking configuration was important to control the unit’s overall size. These crates are perfect and much better than any others I found. Only problem was I had to buy 50 - so I've got over 30 left - if anyone wants to build another one....?
I used concrete pre-stressed lintels to mount the crates with a butyl lining to contain the water. The B&Q storage box is merely a cover and is not structural apart from for mounting the top pipe work.
Click any Image to Enlarge: 
The water flows from the base of the shower straight into the second major change.
The Kaldnes K1 Filter.
The schematic shows the idea. A large through-flow area to give high volume,
low velocity flow through a full 200 litres of media.
The media is not fluidised as I want it to act as a “polisher”.
However, by controlling the level with a standpipe and activating the air system, I can fluidise it for cleaning.
An important part of the top-down flow arrangement is the overflow wear. This
means if it the media gets blocked, all that will happen is that more and more
water will pass to the outlet chamber over the wear.
This is an important “safety” feature.
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any Image to Enlarge: 
The
pictures show from base working upwards.
3. The new pipework.
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Image to Enlarge
4. Cleaning/recycling.
The picture below shows the outlet chamber with a return to the pond and an opening 4" port to allow filter recycling. The pond return can be stopped with a plug.
The standpipe chamber has two filter standpipes, to drain/flush the two in-ground sections of the filter. The third standpipe is from the bottom drain and includes an overflow to prevent over filling in rain.
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Image to Enlarge