Backyard Aquaponics
A place to discuss aquaponics

Would you except don't do it ?

Making a rectangular tank curved and narrowing won't do anything to make the tank self cleaning. What you have is possibly an aesthetically pleasing landscaped shape but it won't be able to handle much of a waste load before becoming fouled with the seriously heavy waste load that you get with even a small number of ducks.

Polyculture (inclusion of ducks) has a place in food production but the design you have posted is not something I would do.

That's probably true, although I was looking at the Tetra3500DHP debris handling pump which supposedly can handle some abuse, and possibly a second waterfall pump in the sump. Another thought I'd had after reading through the low energy aquaponics thread was constructing the island along the lines of a grow-bed/bog-filter fed with an airlift. I don't know how much that's going to do for a 2500-3500gal pool, but as one of several systems it can't hurt.

While I'd like to do whatever possible to get good radial current for oxygenation and breaking down wastes, ultimately this is going to be an open "nature pond" type system with plenty of critters to help deal wiith extra debris.

The tank design I was talking about are designed to concentrate waste to the center drain and remove it for processing (or removal) elsewhere.

What you are talking about is a completely different mode of operation realying on a completely different set of principles and processes to keep it clean.

I've just sealed my bottom draining FT, so I've just got to figure out how to let water through, without letting the fish out.

My Cod are still quite small, probably three inches long, but quite skinny, I think if I had the gap at even 1 cm, the fishies would be sneaking underneath it.

I see the logic in the system, but I'm just paranoid the fish will get underneath it. It's a 90mm drain in the bottom, and when all siphons kick off all at once, it maxes out. Will a 5mm gap at the bottom let enough water though?

Would it be possible to post a picture please?

Did you use a uniseal or bulkhead on the bottom?

Neither.

It's a 90mm elbow. Concreted into the ground.

Could you glue a 90mm cap on the end and drill holes in it?

Pretty easily. I was thinking of putting a 90mm pipe with an end cap, and cutting some slots in the pipe.

I just wasn't sure if Stu's diagram of the bottom draining cap would work better (draw out more solids or something).

I ended up using a pool sump fitting for my bottom drain. http://www.waterwayplastics.com/products/pool-products/drains-and-suctions/main-sumps-3/. I attached a "vinyl liner sump body' to my rubbermaid tank, and ran 2" pipe from there. I plan to put more of a "koi toilet" type lid on it eventually. It also has two plumbing connections - one horizontal, one vertical. The unused opening can be re-purposed to bring an air line in for a central air diffuser.

They also have sump bodies for embedding in concrete.

How would you connect it to a liner?

It has a gasket, a clamp ring, and stainless steel screws. I substituted longer screws (since I was going through the thick bottom of a rubbermaid trough instead of the thin liner).

I do know that the Koi folks recommend that if you're putting a bottom drain in a liner that you need to bed that drain in cement. I assume it has to do with reducing movement, but i'm unsure.

I will try to dig up some pics tomorrow to show you how to do an easy install through liner Stu.
Column: stick a standpipe in the center drain with screen around the top until the fry are big enough, then pull it and install the bottom drain.

While we are on the topic of how to do the center drain...why not use a uniseal? The small bulkhead fittings are ok but the big ones are seriously expensive.

For sizes larger than 6" I've looked at using a flange and ring arrangement but I'm always open to suggestions.

Personally, I use bulkheads up to 6" and van stone flanges above that. Uniseals are good for rounded, low pressure surfaces like the side wall of a tank or sidewall of a 55gal drum. Why not use uniseals more? They don't hold pipes as straight and rigid as a bulkhead would and the overall risk of failure is higher. It is a 1 time buy for the life of the system... Worth it IMO.

Here are a few pictures of the through liner install I mentioned to you. I cut a piece of Plastic to lay under the liner and act as a backing for the bulkhead to tighten down on. This does a few things, first it allows the bulkhead to be tightened without distorting the liner on the last few hard turns. It also helps to get that fitting nice and flat for plumbing where many times it is difficult to repack the dug out area under the drain after you finish plumbing. I had some thick acrylic sitting around but you can also use ABS plastic and it will work good.

Here is that last picture: