What I plan on doing is using a Injector Pump (Stenner 85MHP40) on zone 1 activated by a 110v relay. It will be plumbed in my main feed line just before any zone solenoids. It will not be set as a master pump, just a regular zone named Fertilizer Pump and not set to sequential. When I create a watering program for any zone that I wish to fertilize, I include zone 1 with the time set to a few minutes less, that way it cleans out the fertilizer in that zone line. I can also create a program to water the same zone without fertilizer, I just don’t include zone 1 in that program. Hope this helps.
Sorry, I just noticed that the demo.opensprinkler names had changed before I did the screenshot. Zone 1 should be named Fertilizer Pump and Zone 2 named Banana Trees.