Backyard Aquaponics
A place to discuss aquaponics

I want to make a custom grow bed but am struggling with how to plumb it. Basically an elevated rectangular box with a pond liner. Everything I read says don't cut a hole in your liner for a drain as it can lead to problems.

So how do you get water out of it without a pump? I'm trying to do a custom one to be more appealing and accepting by my spouse

I haven't done this yet, but I plan to do this:



You can see more of Colums system here: http://www.backyardaquaponics.com/forum/viewtopic.php?f=18&t=19967

The other option is a bulkhead fitting rather than a uniseal

Hah, I saw that pic on Pinterest in my google image searches but could not load it. Thanks for link

these people dont know what they are talking about, just cut a nice neat hole in the liner, then holesaw a hole through the bed, then use a bulkhead.

Ok, thanks. I have uniseals, would a bulkhead be a better option? I Don't think it would matter but I'm going to do a constant flood in that.

If doing a constant flood, is there a particular flow rate into the beds or should it just be enough to cycle the waste out of the tank? I'm guessing the more flow the better.

So I just bought some 1.5" bulkheads.

A bulkhead is OK as you can adjust it and if necessary silicone it.
If you put the nut on the outside (bottom) then you should find that the bulkhead 'top' sits pretty low and a standpipe can be easily screwed in or pushed in depending on the type of bulkhead you go with.

Try and minimise the cut in the liner so that it sits nice and firm into the hole (ie. pull it through) then any leaking water wont sit between the liner and the grow bed bottom.
Also try and minimise the hole size you cut. It is possible to use plumbers tape around the bulkhead theads near the top to help get a nice watertight fit.

If the uniseal goes in really neat and tight it will be a good seal but it is probably a bit less forgiving.
I think Colums video above discusses & shows the insertion of the uniseal with the liner (else check his other videos).

** best to fill up with water before adding media and deal with any leaks.

If you're going to use bulkheads I'd suggest making the liner more sturdy by putting a vinyl pool patch on either side where the bulkhead will go. This will stop rips from propagating.

Good advice, thanks guys.

I am picturing a 4x8' bed with 11" of media. This should give me about a cubic yard of volume. My supplier said their haydite is about 1000lbs/yard. I figure 50% of the volume as water and 2000lbs should be a good estimate of the weight.

4x4 posts, 2x8 beam and 2x6 joists should do it, I hope. I guessed a live load of 62.5psf. I put in 80psf to the calculator and 2x6 pine 16" OC says I can go to 7'3". Maybe I should go 8x5... I'm 6.2" and can reach in just fine.

That will give me plenty of media to push my fish population

I can confirm that bulkhead fitting through (EPDM) pond liner in wooden beds are working perfectly fine. Zero leaks so far!

I built my beds with 30*200mm wood, it's more than strong enough for what I need (700*2000*300 beds with lava / scoria).