This was one of the ideas of my own that I liked the most. I'd never heard of a PVC drain when starting this project, so ended up making my own. That's a 1/2 inch PVC 90 degree elbow with a sink filter caulked into it. It's great for keeping fry (fish Babies) out of the filter.
Sadly, it also seems to make the filter suck in air somehow, though I'm not sure how or why. With Canister filters, that can lead to cavitation, which can hurt the impeller (the part of the filter that spins around in the motor to actually pump the water). With my filter, An XP3, I know I can replace the impeller when needed and I've read on several Aquaponics websites that the plants need a lof of oxygen, so I'm wondering whether I shouldn't just allow it to stay on the canister intake or not. I need to do some more research on cavitation, I guess.
This is the Grow Bed. (or one version of it that we've tried.) In Aquaponics, fish tank water is pumped to a grow bed that is filled with some sort of media. The aquaponics kits you can buy for several hundered dollers use baked compressed clay because of its ability to hold moisture and nutrients for the plants to use. I was trying to save money and used the moss and perlite combo mentioned before with some rocks from outside our house, some epoxy coated aquarium gravel, and some pool filter sand. This didn't allow for enough flow to the tank return pipe and the pool filter sand continued to grind skin off my wet hands when I'd try to work with it.
In the setup in the picture, there is one input and one output. I nearly flooded our kitchen several times (and di create several large puddles) trying to get the flow right on this setup. I never did get it right. the Grow bed is proving to be one of the trickiest things to figure out (and I still don't have it figured out yet!)
In these pictures, you can see the outflow plan. I was trying to fill the tank without disturbing the substrate. The muddy water in the second picture shows you how unsuccessful I was.
the grow bed connections were done with Do-it-yourself bulk Heads made by putting rubber o-rings on both sides of the holes I'd drilled in the plastic, then squishing that against the plastic with a female flush-bushing on the inside of the grow bed and a male bushing piece on the outside. That would then connect to a ball valve to try to control flow.
What I should have done:
1. Use bigger PVC for the outflow/drains. 1/2 inch just doesn't seem to drain as well as it should. that small is fine for the inflow, but the outflow needs more help.
2. Keep the holes even. I drilled the holes in an impatient hurry so the hole saw splintered the plastic and made a jagged edge. Just like with drilling a fish tank, if you have any pressure at all besides the weight of the drill (assuming it's a light drill), the hole becomes jagged and harder to create a water-tight seal against.
Also, on the first grow bed version, I put the inflow hole as low as I could on the growbed and the outflow hole in about the vertical middle. I changed this on the next vesion because if your pump stops for any reason at all, the inflow hole becomes an outflow hole and your whole grow bed dries out, potentially killing your seeds. By having both holes at least mid-way up the grow bed, if the power goes out, there's a little water left in there for your seeds. That's for if you want a constant submerged aquaponic sytem. (learn about the different aquaponics systems here). If you'd prefer Ebb and flow, maybe the holes having different heights is what you want.
3. Use More holes.
I eventually did end up putting more outflow holes in. This helped it drain faster, but still with 1/2 inch PVC, I needed a lot of holes. I have 4 in that particular grow bed now and it's still not enough. Plus, with more holes, there's more places that can (and do) leak.
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