Back in the early 1980's I played around a lot with reverse-flow UG's. They were commercially available for sale, but even back then I was a cheapskate with more tools and time than disposable cash. 
My best design was one that incorporated a baffle siliconed into the tank at one end, maybe three inches from the side wall of the tank. It extended right to the top, above the waterline, but had a 1-inch gap all along the bottom. The tank was equipped with eggcrate light diffuser suspended about an inch off bottom, covering then entire floor area of the "fish side" but ending at the baffle. A layer of plastic window screen or landscape cloth covered the eggcrate, and then several inches of gravel.
The tank would have one or more Aquaclear 500 HOB filters hooked onto the end so that they dumped their outflow into that 3-inch gap along one side, behind the partition. The water would then flow under the partition and along the bottom of the tank, percolating up through the gravel and into the water column. The intakes for the 500's were replaced with DIY units made from PVC elbows and pipe; there was a size, I disremember which, that fit perfectly into the "receptacle" on top of the motor unit of the 500 filter. These assemblies were made in various lengths to stretch across the top of the tank and pick up water at whichever point you chose.
I also did a couple where the gap under the filter plate on the bottom was larger, large enough to snake a siphon tube under there from behind the partition and siphon out accumulated schmutz. That was more trouble than it was worth; today I'd probably just install one or more bulkheads on the bottom of the tank and mount valves on them to drain water from beneath the plate whenever desired.
The chamber behind the partition was a great place for heaters, protein skimmers (I used this a lot on marine tanks with great success), thermometers, etc. without cluttering up the tank itself. In practice, the 500's were strictly performing a mechanical-filtration role; all the bio was handled by the gravel.
No, this Rube Goldberg set-up did not keep my gravel squeaky-clean. But, once every couple months, I would stir the gravel vigorously, turning my tank into a 100-gallon serving of fishy latte, and then run my trusty Vortex Diatom filter for an hour or so to clear it up. Hoses and valves and buckets and measuring cups full of white powder...oh my...
Ah...memories...
My best design was one that incorporated a baffle siliconed into the tank at one end, maybe three inches from the side wall of the tank. It extended right to the top, above the waterline, but had a 1-inch gap all along the bottom. The tank was equipped with eggcrate light diffuser suspended about an inch off bottom, covering then entire floor area of the "fish side" but ending at the baffle. A layer of plastic window screen or landscape cloth covered the eggcrate, and then several inches of gravel.
The tank would have one or more Aquaclear 500 HOB filters hooked onto the end so that they dumped their outflow into that 3-inch gap along one side, behind the partition. The water would then flow under the partition and along the bottom of the tank, percolating up through the gravel and into the water column. The intakes for the 500's were replaced with DIY units made from PVC elbows and pipe; there was a size, I disremember which, that fit perfectly into the "receptacle" on top of the motor unit of the 500 filter. These assemblies were made in various lengths to stretch across the top of the tank and pick up water at whichever point you chose.
I also did a couple where the gap under the filter plate on the bottom was larger, large enough to snake a siphon tube under there from behind the partition and siphon out accumulated schmutz. That was more trouble than it was worth; today I'd probably just install one or more bulkheads on the bottom of the tank and mount valves on them to drain water from beneath the plate whenever desired.
The chamber behind the partition was a great place for heaters, protein skimmers (I used this a lot on marine tanks with great success), thermometers, etc. without cluttering up the tank itself. In practice, the 500's were strictly performing a mechanical-filtration role; all the bio was handled by the gravel.
No, this Rube Goldberg set-up did not keep my gravel squeaky-clean. But, once every couple months, I would stir the gravel vigorously, turning my tank into a 100-gallon serving of fishy latte, and then run my trusty Vortex Diatom filter for an hour or so to clear it up. Hoses and valves and buckets and measuring cups full of white powder...oh my...
Ah...memories...
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