Fertilizer injectors for greenhouse growing/RO system

Calvin,

Both Dosmatic and Dosatron have good reputations, so you cannot do wrong either way. I have had both, and never had any issues. I have had customers purchase the Chinese knock-offs from Amazon for a considerably lower price, but I have no idea of their reliability.

It is best to set them up with a bypass, so that if there is an issue with the pump, you can still water.

Like Marni, I originally went with a variable ratio version, but found that I never changed it, preferring to simply change the concentration of the feedstock, instead.

My regimen included fertilizer @ 25 ppm in all the irrigation water, and when I wanted to add KelpMax/Kelpak or Quantum, I just put them in a hose-end sprayer, so I ended up with a blend. When using an insecticide, I bypassed the injector, and still used the hose-end sprayer. (I have no specific knowledge that insecticides are incompatible with fertilizers, that was just a personal preference.)

On the subject of feedstock concentration and pump mixing ratio, there’s a couple of things to consider. First and foremost, don’t plan on an extremely low dilution ratio. As an extreme example, if one were to set up a 25 ppm N solution of MSU RO (~0.18 g/L) by injecting 1 ml of concentrate per liter (1:1000) that concentrate stock tank would have to contain 180 g/L, which is likely beyond the solubility limit.

Generally, a dilution rate of 1:150 to 1:100 is recommended for fertilizers, but the greater to volume consumed, the more stable the concentrate solution will be, but the more frequently you’ll need to refill the stock tank.

If you go with a variable-ratio device, for mechanical reliability, when you settle on a mixing ratio, the pump should be chosen with that ratio in the middle third of their range.

When I first started using RO, I used Dyna-Gro Grow formula, and that dropped the pH like a rock, so I bought a second pump and used it to inject ProteKt to bring it back to around 6. I later learned how little the pH of the applied solution - especially one with as low an alkalinity value as a 25 ppm N fertilizer/RO solution - affects the pH of the rhizosphere, I simply stopped worrying about it.