Backyard Aquaponics
A place to discuss aquaponics

My AQ system is in a greenhouse that gets chilly in winter. Although I have 800W of water heaters, the tilapia have a hard time of it. I'm looking for some kind of hexagonal styrofoam floats I could put on the water surface to retain heat and reduce evaporation. Maybe 6 to 8 inches in diameter, half inch thick. For some reason this seems to be difficult to find.

Does anyone have any ideas? How do you deal with heat loss in a semi-outdoor system?

Thanks for any help!

Hi there!

Can you post some pics of your system? It might help to get the wheels turning.

Warning:The following are ideas, just ideas, from a tired guy who has a few minutes now that everyones asleep!

1. Insulation helps.
2. How do you run your system? Flood and drain vs. Constant Flood? DWC? I think in theory, f&D cools the water, and CF might keep temps a little more stable.


I would think that you don't necessarily need something to float on the surface to help keep the temp up a bit.
You might be able to simply put styrofoam over the whole top of the tank, leaving an air gap between the water and the board. I would think that this might help keep the oxygen levels up a bit compared to the floating method. Blue Board might work for that job.

Heat loss is probably greater from the water surface, but it wouldn't hurt to insulate the sides of the tank if possible.
One of my systems maintains 3-5 degrees higher temps than another, and the main difference is insulation on the sides and bottom of the tank. I do have a cover, but it isn't insulated.

Another thing to consider is possibly turning off the water pump over night, so cold water from the grow beds isn't flowing into the tank, but then you might have issues with the nitrifying bacteria dying off if the grow beds get too cold. Not sure on that one. Then you could turn it back on when it starts to warm up. Are the grow beds insulated? That might help as well.

If your northern greenhouse wall isn't insulated, that might help too.

If the greenhouse isn't too big, maybe you could make a second layer over it? having a gap of air would add an extra layer of insulation. Ideas I'm getting are maybe a metal carport frame, with builders plastic over it?
But I'm not sure how severe the weather is out there.

What are your low temps in your neck of the woods (Inside the greenhouse) ? what is the size of the system and greenhouse? How old is the system? Have you tracked water temps over winter before? How many degrees do you need it to rise?

I am no expert in cold weather Aquaponics, but i have looked into it a bit.

One idea that I have seen that I love involves pumping fish tank water into a big, heated pot of water maintained somewhere below boiling (propane would probably be my choice, but it could work with wood if the setup was right, rocket stove?), that stays heated throughout the night. This is pumped from the tank, through a heat rated drinking water pex pipe that is coiled in the pot, and then discharged back into the tank.

This seems to be a potentially cost saving setup, but it all depends on budget, what can be found a good prices in your area, what you might have lying around, costs of electricity vs. propane, etc. It seems like a system like this would be able to maintain the water at a good temp during a cold snap.

Hopefully something I mentioned might help!

Hmm, some pics of the system and how it's setup would definitely help. Why hexagonal styrofoam shapes? Relatively easy to cut styrofoam if you have the right equipment.

Does semi-indoor mean greenhouse or something else?

By semi-indoor I just mean it's just a greenhouse with double-walled plastic panels, full of 55 gallon drums of water for thermal stability, as well as the 300 gallon fish tank. It's flood and drain, but there's only one tank, the fish tank. The 8 grow beds are filled and drained in sequence (round-robin) with bell siphons and a simple 12V latching relay/paddle switch/electric valve circuit I came up with.

I have 800W of aquarium heaters (and a space heater that I'd rather not run full blast) in there. Turning off the pump at night would keep the aquarium warm but it raises other issues like frozen grow bed pipes.

I do have a cover for the tank but it leaks a lot of heat. I thought if I had hexagonal floats most of the water surface would be covered just by the natural positioning of the floats if I use the right number of them.

Will, what do you use to insulate the sides of the tank? Mine is an oval shape so flat boards would be awkward.

One of my tanks is oval too. Maybe it's the same make/ model. Mines a Behlen.
I really like the shape and size of it. I insulated this one with 2 inch foam.

The other two that I'm working on are round.

I used both 2 inch blue board and thinner white packing foam. I think it's 5/8 or maybe 3/4 inch. My brother in law worked at a glass shop, and got me some nice foam from Shower door packing boxes.

To deal with the curves I cut the foam into strips. a jigsaw works nicely without lot of dust on the blue board. I didn't try that one the white foam. I used a hot foam cutting knife, which works well on both.

I used strips that were 6 inches wide on the round tanks, and I think 3.5 or 4 inches on the oval tank tank since the arc of the curve is smaller. They were cut to the height of the tanks, then held in place with lots of duct tape.

I didn't really clad the oval tank since it's mostly buried. i just added some bricks around the top to hide the foam. The others are getting cladded in wood. I got lucky and picked up a cedar hot that almost fits one round tank perfectly. The other is getting cladded with someone's redwood deck they took out. Gotta Love the free section on Craigslist!! The wood is held in place with ratchet straps.

Looking back at the pictures, I think I might have cut the foam a little wider than I thought. And, I forgot that I also used packing tape on this one, since I ran out of duct tape!

It looks doable. Thanks for the tip!

Knowing the midwest and how cold it can get in some areas you might need to switch your choice of fish to something with a bit lower temperature requirements or just grow tilapia for 6 to 8 months a year and avoid the worst of winter. Just hearing that you're worried about the pipes freezing means that the grow beds and the pipes are a potentially significant source of heat loss.

FYI - unless you're lighting your growing area, once you get less than 10 hours of daylight the plants won't do much if any growing.

I'd try to freeze proof the pipes and shut down the grow beds for the winter. I'd set the system up to run as a Recirculating Aquaculture setup for the winter and insulate and warm the components of this. If you decide you're still going to run the grow beds in winter then try to maximize the heat gain during sunny days and store it if possible (in the ground inside the greenhouse for example). For about 300 to 400 dollars you can build and hook up a solar air heater to supplement your greenhouse heating on sunny days. You're probably going to have to use the heaters for extended cloudy and cold periods.