Backyard Aquaponics
A place to discuss aquaponics

While there has been some debate on the use of UV in the control of detrimental bacteria and fungus (with varying points of view) there seems to have been no discussion on ultrasonics.

I recently got an ultrasonic cleaner (basket type) and there was a warning on it not to stick your finger in when it was running . Mildly curious as to whether this had AP application I found there were a few companies who made water sterilizers. These appear to work by disrupting the cells of organisms passing the transducer and so killing them.
I would imagine it would be relatively straightforward to incorporate and build one of these into the system. The only problem I could see is the formation of micro bubbles (this is theoretical ie I'm guessing) I do not imagine this would be hard to resolve.

I am just passing this on as general information as I do not have the time at the moment to experiment.

That may be fine for free floating algae, fungus and bacteria but I had an issue with a brown, grey bacteria (species unknown) that was growing in long filmentous streamers, inside my bio filter in my large house aquarium. I believe I got the bacteria from an experiment of using fish water to water house plants that drained back into the fish tank. It had to be in the plant's soil as this fish tank had operated for two years without any problems. The only control I could use was to physically remove the long strands but it still clogged drain holes in my mini RBC and grew back quickly but it was only inside the filter so I know it was a light sensitive aerobic bacteria, similar to nitrobactor and nitrosoma.

You're probably right that it came from the soil....noticed a few people lately toying with the idea of adding soil/compost etc to their aquaponic systems...

Personally I think it's a bad idea.... but it their fish...

Unfortunately, Rupe, a lot of things can bring contamination to an AP system- insects harbor bacteria and viruses that are harmful to plants; warm blooded animals that gain access can harbor E-coli; store bought seeds and seedlings can bring diseases as well and even fish can have bacteria, potentially dangerous to humans, growing within the slime that protects them. We can even contaminate our own systems by using equipment that has been contaminated or walking into our greenhouses with insects on our clothing or diseases on our shoes. Also, the nature of a reciculating water system ensures that every part of our system is infected and breaking down a system to disinfect it (as they do with hydroponic systems after growing season) is not a viable option for us either.
Prevention is obviously the best option but not always do-able and control is the worst case scenerio but may be the only option available in some cases. But we must expect these things to happen and have contingecy plans in place. In my case with the bacteria, I knew it's weaknesses and could have eliminated it but it was an indoor system that was soon to be dismantled because the koi and goldfish had already outgrown their tank and are now swimming in their own 450 gallon kiddie pool on my screened in front porch and their previous tank is now empty.

Soil is potentially a great risk, as you never know what you are going to get (I had Portabella mushrooms grow out of a well rotted compost pile that came from a green waste facility) but as I have said before- I know of two ways it can be used safely in AP systems (with a little care) and that is drain to waste or as a capillary raft system, which does not contaminate the water (the water only travels up but not back down).