Hi, been reading and using some of the info, so thought I could share some of my experience, and my current redo.
The ponds are at my dad's place.
So here's the LONG spiel
Pond 1 : Commercial Plastic pool, around 3000 l, and a diy filter, powered by a converted washing machine pump - worked really nicely but was not very ascetically pleasing.
Pond 2 : Upgraded to around 60000l included a waterfall, around 3 cubic meter of small stone in the bottom as filter, worked really well until the first clean up.
Pond 3 : Same pond with new filtration - all rocks/stones were removed and went to a fully pressurized system.... it never coped due to grossly under specified equipment, and then it started leaking.
Pond 4 : Currently busy with a major overhaul, reseal, and conversion to a semi - gravity fed system with my version of a Bottom drain, settlement chamber,pump, mech filter, bio filter, waterfall.
I am open to crit and suggestions especially with the filter design.
So first up a overview of the pond
The pond is a classic swimming pool bean shape, with two shelves for plants initially. The one on the left will be converted to a SC, by building up the wall. Already drawn in the cad model. There is a large waterfall on the right of the pond as well (not shown in rendering)
So after getting all the fish into a holding pond, and emptying the main pond. we found 3 cracks in the bottom of the pond, these were more than likely the reason I was loosing water, so they were broken open, and resealed. After breaking open the cracks, one of the cracks had a nice erosion hollow underneath confirming my suspicions. There was also a pipe cast under the middle of the pond which was removed and floor recast.
Photos shows the recast flooring sections and new built up wall for SC (by corrugated sheets). Some koi after a check up (not great quality sorry).
It was then time to tackle the huge 1000l holes built for the gravel filter, Initially I wanted them filled & sealed but after cleaning out the pond I found about 95% of my "sludge" was being naturally fed into the holes, so I decided to leave the holes and install a version of a BD.
With the debris already accumulating into the hole there was no need to sweep, so a catchment and flush system was needed. this was done with 110mm pipe from each drain into the SC chamber.
The plan is that with a plug that was made by a friend the sc chamber can be sealed off from the pond, and emptied, the plugs are pulled and the ensuing vacuum(pressure diff) creates a powerful suction to remove debris not picked up by the natrual flow.
Pictures shown the installation of the drain, and the pipes into the SC
Now that all the repair work was done it was time to remove all pipes no longer needed, and reseal the pond.
This was done with a commercial sealant available here. The waterfall was also sealed, with what was supposed to a natrual looking color.
It turned out my natrual and the suppliers is somewhat different.
Below is before and after of waterfall, and the pictures of the reseal.
The remaining pipes are for return venturi lines.
So for the filter, here is a model of what my plan is:
There are 5 chambers in total, the first 1 or 2 will be for mechanical filtration, then 3 for bio-filtration (the plan is to have the media in crates for easy install and clean).
If I go for only one mech filter the last might become a polishing filter. (leaning towards this)
The water will go under and over to force the water to pass through all media.
I still need to decide on the media for both the mech and bio
Still to be done :
build of filter
Install of pumps
and return to waterfall