Circular/linear River Stream Biotope

[biodives]

This thread doesn't fully fit any of the forum topics but since it will have plants I've decided to put it here.

Now that my planted Orinoco biotope is running smoothly I am looking at starting a second tank. So far I am just in the planning stage but I have not been able to find any examples of the tank I am planning to build which means it is either a stupid idea or it is original (or I am not good with Google). Anyway, I thought I ask here to see if this has been done before and, if not, if there are good reasons not to even try.

The motivation is to recreate a river stream where all water flows linearly in one direction. In typical aquariums the pump creates circulation that bounces of the glass and flows in all directions, which is rather unnatural. There are a few web pages that discuss such a tank with (powerful) pumps on one end and water intakes on the other, connected by under-gravel tubing. This gives a semi linear flow but with ugly pumps and sponge-covered inlets on both ends. It also feels unnatural to me that the "river" starts and stops at each end of the tank.

The tank that I have in mind is a 48x24x12 inch "coral fragment tank", apparently used to grow pieces of coral. My plan is to put a 3 foot divider right in the middle, or perhaps a wider center island acting as a filter/aquaponics with emerged plants on top. This separates the tank for the middle section but both ends are connected. So seen from the top it looks like a squarish "O" with circulation pumps on each end to create a linear water flow that circles around. See image below.

The aquarium can be viewed from both sides giving two times 4' of river habitat. I could also place the separating wall a bit off center to give a narrow side with high flow rate and a wider side with slower flow rate. In the image below I have placed both pumps on the narrow side which is the side close to the wall where they will be less conspicuous.

I have a nice spot separating my living room and kitchen that is just the right size for such a tank and with wall outlets in the right place. I would still have to think on how to light the tank and whether to have a simple central divider or a filter/aquaponics centerpiece. I would place giant hairgrass and some long stem plants that bend with the current along the river bed and possibly some plants that grow over the edge of the centerpiece and float along the water surface. I don't plan to make it a supercharged current (though that could be nice for loaches and other critters that like turbulent rivers) but certainly one that is more prominent than the general planted or community tank.

Anyone seen something like this before? or having suggestions that I haven't thought of?

[jvision]

I've built a few ponds with wetland filtration, which is what I picture you're wanting to build here - if I understand your plan correctly, you'll have a wetland/aquaponics area in the middle to act as filtration for the system instead of an outside source (like canister, HOB, etc). You'll want the middle section to have some decent flow through the substrate, or you'll end up with anaerobic sludge... not at all what you want for true aquaponics, which relies on high O2 getting to the roots. However, in a wetland, you do use anaerobic activity to denitrify the system (but, that's what the plants are for in the aquaponics system).

The easiest way to have flow through the middle would be to lay down some bubble wands and run an air pump... I would set up some kind of shelter (like PVC cut in 1/2 and drill a bunch of holes) for the bubblers or else you'll have to dig up the whole thing when they get clogged. You could also use one of the pumps to flood the middle - pump water to the surface and have it seep down through the substrate - but the challenge may be in making it look good. With the bubbler, you can hide everything easy enough. You'll want to heavily plant that island to cover all of the surface, or you'll eventually have algae covering it... laying down a layer of (Java, flame, Chritmas, etc) moss or Riccia would be a good idea.

I would use a porous substrate like 3/4" lava (cheap at landscape suppliers like Burnco or Canar) or Hydroton (expensive at hydroponics stores) - it'll house a TONNE of beneficial bacteria.

I don't know anyone who's actually done this... the closest I've seen to this type of concept tank is in zoos/aquariums. I'm curious to see how/if it works!!

[biodives]

Actually the central filter/aquaponics idea isn't the main focus. It could just be a thin sheet of (black) plastic or something that more closely resembles a river bank. I just need something to separate the front and back halves of the tank so the water will circle around it. The filter/aquaponics gives the separator another useful function, but it also reduces the amount of space left to the fish, so I may be better off to keep it simple. What I'd like to know is if a "linear-flow" river biotope has been set up before using a central separator with the water flowing around it in circles.