Backyard Aquaponics
A place to discuss aquaponics

The entire box is 4' deep, 4' wide, 20' long, but the growbed is only the top foot (30cm) by 16' (about 5 meters) of it. The area under the growbed is a deep, dark cave that the fish love.

Access for feeding, light, etc is at one end where about 3' (one meter) or so is left open.

Water volume is about 800 gallons (3000 liters).

The concept was that by building an insulated and compact system I could minimize heating costs (I was going for tilapia) and prevent temperature fluctuations. This worked well: the max temp change I've seen in a day is under 4 degF (2degC) and I could keep tilapia alive and healthy (although not feeding well) with a couple hundred watts running 24/7 for the two coldest months, even when temperatures of the nearby swimming pool stayed at least 20F (10C) colder and often fluctuated by nearly 10degF in a day.

Unfortunately, the water will only stay at best temperatures for tilapia for a week or so in a normal summer here and this summer was so cool my two trout did fine, with a couple weeks of having a fan at night to cool the water. Catfish and goldfish also do well.

The biggest disadvantage is that I can not see the fish well without putting on mask and snorkel, putting a flashlight in a plastic bag, and going in. Pitch black and there is only about 6" (15cm) of air space between the water and growbed in the cave. A fish might die and I won't see it for days and I can't see behavior to see if they are well or not and can hardly ever see them feeding.

what material did you use for the insulation?

1.5" (40mm?) foil-faced polyisocyanurate on the sides and bottom of box.

I would have been happier with styrofoam, but couldn't find it. Since then I've found it at Home Depot.

I haven't seen a sign of any fish in the big system for about ten days, so, despite 48degF (9degC) water temp I grabbed wetsuit, mask, snorkel, and flashlight and went in to take a look. Fish were all hiding at farthest end of the cave, looking fine and healthy. Even the trout was there, looking like a monster with the magnification from the face mask.

I missed-out on the last day of abalone season, but at least I can dive in my fish tank!

snorkeling in 48 degree water... now that's where I draw the line =)

Alas! My temporary measures have failed and fish died.

The bottom of the tank is plywood on gravel, lined with plastic. A month or so back I began to find juvenile rats floating in the system and the catfish lost appetite. I took various measures including salt and changing water, a week ago the entire population of about 12 catfish (about 40 or 50lbs total) went belly up. The goldfish are still fine.

My theory is that the rats created a nest under the system and, while creating some additional living space, chewed through the plastic and found themselves in a deluge. The worked their way upward toward the surface, but in this case it led into the fishtank where they drowned. Perhaps one is still plugging the hole..

Anyway, things were decaying already and I have much better ideas for future construction.

Lessons learned:
Catfish love dark caves and it created a nice compact system, but one really needs to be able to inspect everything.
if you are in an area like this (near sources of rats), make stuff ratproof
any wood that gets wet must be able to dry out.

Might try Essence of Peppermint. That stuff is strong. We used it in and around our bales of hay a couple of years ago. Haven't had mice/rats in the hay since then. Dab the stuff on a few cottonballs and toss them where you think they might be hiding.

Try planting some mint in wicking beds.

If you have a local zoo around, there might be the possibility of getting some "Litter" from the bobcats cage. Put some small buckets of that around (if it doesn't stink too bad).

Roofing steel encased fishtank and growbeds?