Backyard Aquaponics
A place to discuss aquaponics

According to Timmons and Ebeling, there is no appropriate angle for fish waste removal. They say:

So is there no advantage to using this type of tank?

Heres a simple line drawing, but it shows the general idea

https://docs.google.com/drawings/d/18AhTtIjg_VHthiA6kh-E16E10vcDWNJIDcJCryEmLec/edit?usp=sharing

No advantage. Putting a drain in the center of a circular tank, and making sure there is a rotational current will concentrate the solids into the center drain.

As a FT? No. Hence why I asked the question about why you wanted to use this style of tank.

Seeing Nate and Co. use these tanks for their fish made me question the rest of the information they publish. After all if they could make such a simple aquaculture engineering mistake it implies they are not as knowledgeable as they purport to be. Or rather when they built that system they didn't know much about fish, after all to be fair they could have improved their knowledge by now.

When I see information from a source about something I know about which is wrong it makes me doubt the veracity of the information I don't know much about. In this case I know aquacultural engineering but my knowledge of plant hydroponic nutrition is not as good.

Those tanks are good for use as radial flow filters or swirl filters though.

Stuart, if the conical tanks work as a radial or swirl filter by collecting solids at the base outlet, why would they not work as a FT?

"engineering mistake" seems to be a bold statement, have you inspected their tanks to determine that the conical bottom prevents the collection of solids?

Maybe they have designed the flow of the conical tanks to collect fish waste in some way we are not aware of?

Like many things they will work but they won't work as well as other options.

Many people think that conical bottomed tanks are best or even required to remove solids from the FT. As someone else posted above this just isn't so. FTs can even have an inverted conical base ie the bottom slopes up and they will efficient remove solids from the FT.

One of the reasons such tanks work well as SF or RFF is because of the fluid dynamics of the tank. Note though that when they are used in this manner the effluent from the RFF or SW goes out the side and not the bottom. When these tanks are used as FTs if they are installed in such a way to periodically remove the solids after they have collected in the bottom the waste will be continually sitrred up by the fish. If they are installed so that the water drains continually form the bottom then they can create a vortex that is too strong for the fish to swim against. If they are installed so that only a small amount of water goes out the bottom you will avoid this problem and the tanks will work just fine but such a tank is much more expensive to build than a regular AQ Cornell dual drain tank.

I stand by the mistake comment but I never said it wouldn't work.


It is possible

I've not heard Nate Storey recommend conical tanks for fish tanks (has he?).

Could be several reasons why they are using them. I'm using one cos I got it cheap. Its true that solids don't accumulate at the bottom as to fish stir them up (fish tend to hang out at the bottom), though I do find that pulling a percentage (about 30%) of the flow from the bottom helps get the solids out, and more come out that way than through the other take off points mid way up the tank.

The biggest issue I've found with solids collection is the air stones causing an upward current that pulls solids up with it. this is why the koi guys have centre drains with air injected directly above the drain.

I find I actually get better solids collection in the bottom of my flat round tank, though the pumps struggle to clear them.... a SLO in the middle would do a better job I think!

Exactly. Which is why the AQ tanks are designed and installed that way.

I thought the idea was to remove the solids rather than "collection in the bottom of my flat round tank"

Forgive me but I can't imagine how having a round conical tank with a SLO in the centre can be worse at collecting solids than a round flat bottom tank?

why do the solids sink to a flat bottom tank but not to a conical tank?

It has to due with the tangential and radial flows created within the tank when using a center (or double) drain and properly designed water inlet manifold. Waste particles are forced down to the flat bottom, then across to the center drain. With a slope they are still forced down, but then because of the slope the flow that would normally carry directly across the flat bottom has to interact with the sloping geometry which IMO is less efficient.

The other thing nobody had brought up is the added difficulty of harvesting fish. Have you ever tried to stand on a slimy sloped tank bottom? Instillation is also much more difficult.

I don't know anybody in aquaculture that uses sloped tanks for culture vessels...

Too right. I had just thought about the difficulty of getting them out of a silo like tank. The thought of ever having to go in there is not a pleasant one. Now that you have brought that issue up I don't think I'd use one of these for a FT even if it was free.

It seems to be that at first glance what looks like a good idea but in realty has no benefit at all.

so conical tanks just add a lot of complexity for no gain and a lot of negatives.

Very interesting, I never would have thought. Ive read stuart say it a few times but I didnt believe him

LOVL THPTTWHAWSF.

So I now have a little more credibility do I

Ha ha, just a little, dont get a big head or anything