There are many ways to build a false bottom. I've tried several and they all work well, but recently did one using slabs of hydroponic media, which is rubberized cocoanut fiber. I built a box of this by tearing it lenghwise into about 1 1/2 inch strips and siliconed these into the shape of the tank, leaving some space against the glass to fill with gravel to hide the media. This was then topped with the full width slabs supported with short pillars of pvc. Any other substrate you use can go on top of this with or without more screening material such as the weed inhibitor cloth that has small holes in it for drainage, but keeps the soil substrate from leaching down into your false bottom. You can leave open places, also lined with pieces of the hydroponic stuff for pools and also line a separate pool for your pump.
You'll need something like a 600 Rio pump and tubing to go to the top of your falls. The falls can be designed from rock, cork bark, or in one place I have bent the tubing to go along the top edge of a fern bark panel and sealed the end of the tubing with Silicone. I punctured holes along this so it most of it just seeps over the panel the entire length, then added Java moss, some clinging ficus and am getting some spontaneous growth of some small ferns. The spores were probably already there. It is capped over with cork bark that directs any water from the holes that tend to splash, downward into free-falling water.
Wherever you put your pump, usually in the back, you need to keep it accessible in case of clogging or failure. In all but the hydroponic tank, where I just line the place for it, then fill in with smooth rock to hide the pump, I have used a separate refrigerator storage container punched full of holes so the water can get in and out, but the rocks covering the pump don't scatter all over the false bottom. You can invent all kinds of things to do.
For water changes, I simply siphon off the water from one corner using an aquarium air hose and replace it. You may need to do several water changes after the initial set up, as it tends to foam at first. The water will almost invariably be brownish if you use cork bark, fern panels or the falls splash through some of your upper substrate. This is harmless and gradually lightens up. To some people, this is esthetically unpleasing if you have open pools where the color is obvious. The photo is of the tank right after I set it up, so is relatively barren of foliage. The link is for the hydroponic Coco Tek Grow Slabs.
Let me know if this is too confusing.

Link
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus
2 D. azureus