Backyard Aquaponics
A place to discuss aquaponics

In planning my system I have been having a debate with my wife about which would be better, to have the tank in the ground or sitting on top of the ground.

We will be building a greenhouse and want to set up similar to the S&S model. We want to keep the water in the fish tank as constant as possible. A black 800 gallon poly tank sitting on top of the ground will absorb the Sun's heat and retain it at night helping the greenhouse stay warmer during the colder nights. The same tank in the ground would seem to hold whatever heat it has longer because the ground acts as an insulator, but would it be able to heat up as much being that it is in the ground and the Sun can't shine on the black tank as well?

Add as an aside that I am not sure if we should pay the money for the huge black poly tank or go with the galvanized type that Joel has in his setup. I guess the answer to the first question will help me decide what to do about this.

So which would be better in this circumstance?

a couple of questions back to you John.
What is the ground like to dig? We have LOTS of rocks, but enough space to bring in heavy machinery to shift them. Will it be easy to dig and bury the tank? What are the dimensions of the tank?

Jaymie
Well the ground isn't a problem although it is compact. And the black poly tank in question would be 7 feet in diameter and approximately 3 feet deep. the galvanized alternative is 7 feet in diameter but only 2 feet deep.

personally I would go for the deeper tank if you can afford it, better depth for the fish and more water bulk to maintain temps etc.
I'm not really sure on the burying or not (we don't get any where near as cold as you guys)
If you left the tank unburied, you could wrap it with an insulation of some sort (bubble wrap or panda plastic)
Does your ground freeze?

Will stand corrected if need be....

Most of my reading here John seems to indicate that it's the growbeds which attract and add heat to a system and reflective heat from "uncovered" tanks (particularly overnite) that lowers temperatures.

To me black poly would obviously heat during daytime. If covered at night I would expect that most temperature would be retained.

Some have suggested that you wrap the tank with "insulation bats" or similar.

If your daytime temps are cool-cold you could cycle some of your system water through black poly tubing on top of your greenhouse to heat the tank.

Fortunately or otherwise here in Australia we're usually looking for ways to cool rather than heat.

Obviously depends on what the optimum temp range is for your species of fish as to what approach you take.

If your greenhouse/location has good thermal mass (ie passive solar) then as long as you perhaps have some way to cover at night (floating rafts maybe) then I don't know if there's a lot to be gained (thermally) from burying the tank.

However given the kind of winter temps you guys and gals face in some areas of the US it might be a very sensible thing to do indeed.

Janet's been through a few seasons by the sound of it, so I'm sure she can relate to your area and circumstances better than I can.

Lots of reading threaded through this forum on the subject.

Jaymie, Our ground freezes but not very deep, few inches I would guess at the most.

My goal is similar to most I would think. I want to be able to sustain fish year round but also plant growth. I realize that this means I will need supplimental heating, but how much I need it will depend on the choices I make in planning this system.

I am probably going to have Yellow Perch for my fish and they can handle cooler water temps with little problem. I am expecting water temps to drop overnight especially this time of the year, but I wonder which method will allow the temps in the greenhouse to stay above the freezing mark better, in ground or on it or will it matter?

black poly for collecting heat is dubious. If you want to keep your tank temperature more even, put insulation around it. a 2.5m*1.25m*40mm PS foam board costs $25. I haven't bothered, and I've found that with 4.5kL in a greenhouse the temperature doesn't move much unless you force it with some kind of heat exchanger or solar collector (growbed).

Apart from the temp, if your tank is above ground all your grow beds need to elevated above the high water level for a gravity return, or else you need a second tank/pump buried as sump to pump back to fish tank level. If cost out the structures to elevate grow beds or the second tank/pump (also being a second point of possible failure), burying may seem more attractive

Or, you run the system open loop :
http://njhurst.com/~njh/blog/20061220
http://njhurst.com/~njh/blog/20061230
(DC = aeldric)
and gravity feed everything!

IMHO if you're going to run to waste with an open loop you might as well just go hydro, the returns are better.

Part of the attraction of AP to myself is the closed loop concept.

Also have to wonder if an open loop is really environmentally sustainable or friendly especially if it's being directed down a drain and/or into our waterways.

Now if it's being used to "flood" a soil based garden at least it has some benefit, but I suspect that this isn't a practical solution here given that your winter periods involve frozen earth cover.

If you had read those links you would see that pouring water down the drain is not what is being discussed. Before critcising an idea, at least RTFA.

I'm sure aeldric can defend open loop better than me, but the basic idea is that fish water is already approximately the right concentration for open loop control such as with the autovalve, and the resulting water removal rate is no different to closed loop once you factor in transpiration and plant building water use. (Hence open loop can use less water than closed loops, have much simpler control mechanisms, avoid pumps, prevent disease etc)

No personal criticism intended njh... the autopot/autovalve idea is an extension of many similar hydro ideas.

Traditionally hydro has been run to waste and "open loop".

If the autopot/autovalve is re-circulated back to the fish tank then by definition surely it is "closed loop"

From reading your blog I interpreted your system as "open" loop with no return to fish tank.... sorry if I mis-interpreted your intentions.... will happily stand corrected and learn at any time...

Still stand by my comment ...



... stress IMHO

Njh, I've read (again) the first part of the blog. Is it possible to get a diagram of this set-up? I don't think I'm getting exactly where the water is going (to/from/round-about). It sounds intriguing, but I think I'm missing it

Ok, I'll do a long post when I get home tonight. Suffice it to say that at this stage the ideas are sadly mostly hypothetical, with the exception that we have evidence that open loop autopot thingys are efficient users of water and that the plant water uptake roughly matches the nutrient uptake. So water neither goes to waste nor back to the plant, instead being entirely used by the plants for transpiration and food storage (photosynthesis).

Roz, can you explain why you believe dumping is important, and why hydro with fish waste for nutrients is not AP?

I too, am ready to be corrected as I'm probably the most inexperienced hydro grower on this forum (having never grown hydro in a standard system).

njh, think we've managed to misunderstand each other...

Not advocating "dumping" at all, completely opposite, I think the whole benefit of AP is that it's self-sufficient and closed loop.

I'm completely hoping that hydro with fish waste is feasible as that's exactly what I'm proposing to do, only unaswered question seems to be the possibilty of "clogging" with traditional hydro/nft equipment.

So far it looks like several other people here are doing or planning similar things and results so far look really positive.

Personally I see great applications for AP with traditional nft/hydro equipment, myself I'll be incorporating some hydro style siphoning "dutch" pots and an adapted hydro tower.

Your post clarifies your intention for the use of the autopot and I think I better understand what you mean by open loop i.e no return to tank as pot/plant uptake is utilised by (x) number of plants/pots + losses due to transpiration... equal water output from fish tank ... therefore "open loop"

Have I got your meaning now??

One question though, wont this involve (over time) loss from the fish tank and requirement for regular top ups, or am I still missing something.

Concern with regular (albeit small) water loss from tank, either with pumping or gravity feed, is potential for tank level to drop below a level to sustain fish or levels of ammonia, DO to rise rapidly particularly on hot days....

Have been re-reading "Alderic"'s thread and there's merit in what you're attempting to do, especially the aspect of minimal power, effort, intervention etc