These were the tanks before I installed them, they are two identical filters, supplied by a header tank. The tanks were quite cheap when I bought them from a plumbing wholesaler, as were all the tank connectors and numerous bends and the pipe. I drove down to Telford and bought the flowcore from the little factory where it was made.
There's a support frame round each of the top tanks as a third of the tops have been cut and can be removed to give better access to the interior.
The top tanks are on the left. The top tank connectors are for the water in and the ones halfway down are for the water out to the lower tanks.
The water enters the lower tanks from two connectors not yet fitted on the top of the lower tanks and the connectors on the end of the right-hand tanks are the returns to the pool.
Inside, the bottom tanks the water flows out via the reverse perforated spreader bars. The pipes before they leave the tanks, have sideways on "T" connectors in them, as with an open top end it prevents syphoning.
They two top tanks each have double spreader bars to distribute the water evenly across about 5sq ft of foam sitting on a cut-down perforated plastic bread delivery tray sitting on the flowcore, which fills half of each top tank.
I rarely clean the foam as it doesn't get that dirty, probably once or twice a year, the dirtier it gets the better it works, but there are overflows, just in case and both tanks are connected at the top so that if one tank does get clogged the water would first be transferred to the other before it would reach the overflows. I've never had a problem, but I have had to change the foam twice in 25 years as it does degrade after many years.
Then 2 "reverse perforated spreader bars" sitting under another tray at the bottom of the top tanks transfers the water to the tank below. The fifth connector is the overflow to the second set of tanks.
This too has has 2 spreader bars in the top and is full of flowcore. Two full length reverse perforated spreader bars in each under another perforated tray and full tank of flowcore, transfer the water back to the pool. These tanks are sealed.
This arrangement prevents any "tracking" of the water in the filters. I've also a drain in each of the bottom tanks connected to a shared valve which enables me to clean them out a couple of times a year of any silt that collects. I've never had any water leaks from this system. It looks after itself for the most part.
Here's a diagram of the pipework inside the filters. The overflow shown is in case the foam in one bank or the other gets blocked, there's another not shown set higher, that would return excess water to the pool. The diagram only shows one set of pipes, there's two sets in each bank. I think I got the "tracking" situation covered.
This is the return to the pool. I'm just trying it out here to make sure the pipes will fit where I wanted them. After taking this photo I made "S" bends with polypipe sweep bends, fitted to the pipes where they leave the garage on the left, to lower the pipes below the level of the path, before I remade it and put the bridge back. You can see the pump sump in its concrete "block" the top of the plastic barrel is about 4" below the cover which now fits the concrete collar.
The drain pump acts as an overflow, but I've a skimmer connected to the same drain that I use as an overflow near the bridge which acts as an alternate way of letting water out of the pool. The height of the water in the pool can be regulated by adjusting the height of the skimmer, or the drain pipe connections in the sump, so I can trickle out either, "top, or bottom water" I usually let it trickle out from the drain pump, I constantly trickle change this pool at a "dribble rate."
My bottom drain "kit." I made the standpipe from a piece of the key terrain. I made the seal at the end of the standpipe with an applied fibreglass ridge and a Hoover belt. Works a treat.
I laid the patio myself. It is built on top of a concrete raft. I had to grade the York stone slabs to achieve a fall so it would self drain. It drains to both sides of the patio and dries within minutes after a rain shower.
This is my Oase 8,500 pump, (new in a box on eBay for just over a hundred quid, beat that!) with a home-made connection for the waterfall. I prefer a sweep bend to the universal connectors supplied, as I think they impede the water less. I bought it last year as I wanted to reconnect the waterfall. (a compromise as my wife originally wanted one of those naff imitation rock patio water features and I wasn't having it).
It replaced an Oase 5000, which was still going strong after ten years. I'd never have any other submersible. I keep it as a spare and for the winter months when I don't run the waterfall. I have another small pump as a spare for the drain pump.
汗流满面，一字不懂 
