Sterile vs. biologically active nutrient solution

[ian]

I have had experiences with both of these methods. There is some debate on the internet about which method is better: using a totally sterile reservoir or a reservoir containing beneficial bacteria.

For sterile solution, I have used the easy way of sterilization.  The easy way to me is bleaching equipment, using physan 20 to kill off algae on the walls of the greenhouse, and running strong (5%+) hydrogen peroxide followed by plain water. Maintenance is done by a tiny bit of hydrogen peroxide on a regular basis. I probably waste a lot of hydrogen peroxide like this, but it is not really that expensive when purchased in large bottles.

The downside I have always encountered with sterile solution is that roots eventually require trimming or they start turning weird colors. This compounds when tubes/misters get clogged by roots, which in turn lowers the flow rate, which results in bad bacteria showing up. I have tried boosting oxygen content way up but there still seems to be some bad effect, especially with root systems that occupy 5-10 gallons of space per plant.

In contrast, the relatively expensive (as compared to hydrogen peroxide) beneficial bacteria and enzyme solutions take care of this problem for me. I have used the General Hydroponics Sub Culture and Botanicare Hydroguard to inoculate nutrient solution. As well, I have tried Humboldt Nutrients ProZyme and Mayan MicroZyme products. In my experience, roots which are treated start to finish in a beneficial bacteria slurry are always clean and have a new growth appearance. The old or damaged roots dissolve into the solution, leaving leftover root particles on the bottom of the reservoir. At first, I thought this was algae, but it definitely is not.

The other method I have tried to generate beneficial bacteria is to use a recirculating deep water culture system which pours the water over a growing medium "filter" upon return to the reservoir. Lava rock is the best for this, although I have tried expanded clay and coco coir with success. The idea is that the beneficial bacteria get a highly oxygenated space of their own to colonize. The colony "appears out of thin air," at least in a greenhouse.

The biggest drawback of the beneficial bacteria system for me is the cost. I have found that it is less effective in aeroponic systems where there is no growing medium than in any system with medium. I have had best results in recirculating systems with a high rate of water exchange (10 / hour).

I can't seem to find a lot of information on google including google books and scholar about experiments. I have found a few debates on the net which basically amount to why would you put a bunch of bacteria in your nutrient solution, but I'm not convinced of there being any reason not to.