Backyard Aquaponics
A place to discuss aquaponics

I have the fish tanks under ground and it proved to be very efficient in controlling the water temperature, makes it warmer in winter and cooler in summer. I am expanding my system and the new system the fish tank has to be the highest point in the system so I am thinking of covering the tanks with with mud/earth. In other words raising the ground to cover the side of tanks. Will that still work in summer or will it make the water warmer?

I think it would help insulate the tank still although it would warm faster than the ground since it's like a raised bed. Maybe run a wire fence about the height of the tank, all the way around the tank in a circle, maybe a foot or two away from the sides and fill between them with earth. This might give you a bit more mass to heat up or cool down. If you do this, you might want to leave a cutout for better access to the pipes (you could fill this with straw for Winter to help insulate the pipes).

Come to think of it you might be able to use straw bales instead of fence I'd still put earth in near the tank though but you might want to check out BuildItSolar.com they know a lot more about this sort of thing than I do - http://builditsolar.com/Projects/Cooling/EarthTemperatures.htm

On that link take note of the section on Heat capacity of soil. What it tells you is that dry soil warms and cools faster than wet soil. If you could wet the soil around the tank to keep it cool ... you get the idea I think.

I might post this up for some of the people trying to get their fish through a hot spell.

Will the new fish tank be in the shade? If you cover the tanks with earth and they're in the sun all day, I doubt it will do much to keep temps down.

It must be shaded if you want to keep it cool in summer.
I've just put a ring of steel reo supporting shadecloth around my 9500l tank, which is partially buried, and filled in the gap with river gravel, which I spray with a hose every now and then to provide a cool barrier around the FT, but it has to be kept out of direct sunlight to stay cool. We'll plant grape vines over the top for shading and they will let the sun through in winter, when a bit of heating is handy.
Right now it is 31C and bright sun on 8 2 X 1m GBs (lots of plants, and most exposed areas have some insulation over them), and the water temp is 19.4C. I still need to bury some pipes, some are shaded, some are in the sun, and the ST is buried but also in the sun.

Why does the FT need to be highest point in the system, again?

I'd assume so that the water can exit via a SLO into the GBs.

kinda scares me to think about a drain in the fish tank that could empty the tank via gravity in a plumbing mishap

Soil/earth doesn't really insulate. It sort of does but what it really does is provide extra thermal mass. Heat travels through earth at about 1"/hr. Therefore for the earth around the sides of the tank to work effectively to keep a system cool the thickness of the earth needs to be at least 2" for every hour that the wall is exposed to the sun/heat.

The reason it is 2"/hr is that when the earth gets hot the heat travels into the wall. After 12hrs of sun the heat would travel ~12" into the wall. When the sun goes and the temp falls the heat keeps traveling through the wall. Half of it starts moving out of the wall the other half continues to travel in.

To keep a system warm you need much thicker walls.

I'm pretty sure that most of us have the FT as the highest point of our systems.

+1 poor choice of words on my part, the thermal mass is way more important. It apparently does have some insulation value but it varies and depends on void space and water content as well.

Dry earth is a far better insulator than wet, and has a much lower heat capacity.

Brian, if a SLO has a vent as the highest point of the inside-tank piping that can't be blocked, then there is no danger of draining your FT.

I have my FT as highest point in one system, and lowest in the other

Insulation is a kind of imprecise term. Earth is definitely an insulator relative to stone but then so is stone relative to metal.

As G said dry earth is a better insulator than wet earth but calling even dry earth "insulating" relative to polystyrene or purpose made insulation is a real stretch of the term.

SLO's cannot do this as a properly made one will not allow a siphon.

However funnily enough at the end of mutiple 40c days, you can dig downward and hit cold dirt much sooner than 30cm.

When i finally move out of the shitty city, i will have a house made of shipping containers covered in a mound of dirt, im thinking 30-40cm is enough, what do you think stu?