It is very difficult to sterilize the nutrient solution to get rid of all bacteria no matter what you do, there will be always new bacteria entering the system from different sources. By changing the nutrient solution every two weeks and by flushing the system with pure clean water, bacterial population will go down and will cause no harm.
This problem exists usually in a circulating nutrient system.The solution to this problem is to sanitize the whole system before the begining of growing new crop, using diluted Sodium Hypochlorite followed by flushing the system throughly with pure clean water to get rid of the chlorine and sodium residue. Changing the nutrient solution every two weeks will also provide the plants with the right EC and a balanced nutrients.
Regards,
Safwat

jsmith,

Have you looked at the possibility of using Consan 20?

MM

I have no noticeable bacterial growth in my nutrient and haven't for many years in my recirculating aeroponic system.

I pour out 5 gal of muinicipal water and treat it with hydrogen peroxide to 500-1000 ppm. This water sits at least 48 hrs before use in nutrtient reservoir. I mix this water with nutrient/ph correction mix and put it in the reservoir to top up.

At 2-wk nutrient change interval, I wash nutrient tank with 1000 ppm hydrogen peroxide. At 1 month nutrient change interval, I pump 1000 ppm hydrogen peroxide/water only mix through pump/piping/return/reservoir system.

Hydroguard which contains bacillus will clear it right up.

What temperature is your reservoir? Every bacterial problem I have ever encountered was due to high temperatures (above 78 degrees).

The hydrogen peroxide suggestion by Willard is excellent.