55 gallon blue barrels buckle
They seem to be an inexpensive way to build a system, however, they have challenges. The buckling means you need to build a good structure to hold them.
55 gallon blue barrels are round
I know, duh! We went in knowing they were round but not realizing how difficult building siphons would be with a round bottom. We've made it work but they are a bit more fussy than systems with flat bottoms.
Aquaponics is truly an ecosystem
I knew we'd have fish and plants and bacteria in the gravel. But I had no idea of the other insect life who would take up residence in the system. I'm assuming they are good and I don't bother with them. When I sit and watch the top of the gravel as the bed fills with water, all these little creatures come swarming to the top of the gravel. When the bed empties and the water recedes, they disappear. Of course, we also have pests such as white flies and we had a few aphids.
Because an aquaponics system is a closed system, you can't use any kind of chemicals or most organic "solutions" for pests. My approach has been to just let it all be. The only thing I've added are hanging yellow sticky traps to catch a few of the whitefly. The rest seem to be finding a balance with predators. It was a bit overwhelming at the worst, but by leaving it be, it really has gotten much better.
Cycling a system can be very stressful
Once a system is setup and in place, it has to be "cycled". Cycling is the process of growing sufficient quantities of the right kinds of bacteria to convert the wastes, specifically ammonia, in the system into usable nutrients for the plants. If there is a consistent source of ammonia such as a few fish, the cycle will typically take about 4-6 weeks to complete. You can speed up the cycle by adding water and sludge from an existing system such as a friends aquarium, pond or another aquaponics system.
Not all plants love aquaponics
We ended up pulling the citrus trees out of the system in an effort to limit some of the bug infestation. They attracted ants that are not friendly to citrus trees and it was easier to remove the trees than the ants.
In our system garlic and onions did not do well. Potatoes tried to make potatoes all the way up the stem because of the humidity. They were green, of course, and they never produced any usable potatoes under the gravel. I must say, the tops were beautiful.
Tomatoes and peppers grow lavishly in the system as do greens of all kinds such as lettuce, chard, and spinach. When humidity isn't too high, cucumbers and melons do very well. We've grown multiple crops of radishes and enjoyed beet greens and basil.
Many people do well with cole crops such as broccoli, cauliflower and cabbage. I think we need to purchase some "summer" varieties and try again as ours haven't faired too well.