Space itself. I believe there are other intelligent life forms out there and some of those happen to be close enough to communicate to each other/discover each other. We just hit the unlucky(or lucky) spot that we are simply too far away.
I used Jacks Hydroponic 5-12-26 Part A and part B. Idk if it’s my climate(10a) but it’s all I’ve had to use. I have also had no issues with multiple plants in the same tower. I’ve grown fruiting and leaf plants at the same time. I don’t use bloom nutrients. I’ve been doing this since ~2020. I found through trial/error that keeping ph at ~6 and my EC at ~2.5 everything just seemed to grow without issue lol. I always grow in season and don’t try to start lettuce in the middle of a hot summer for example.
Currently growing 3 different cucumbers(lemon,marketmore,Persian), jalapeños,Thai chilis,bell pepper, banana pepper, tomatoes, some butter crunch lettuce that hasn’t bolted yet surprisingly,broccoli. All on the same stand and getting great harvests! I keep ph around 6.5 and EC around 2.5. Im debating going full hydro for everything except trees/bush/root veggies since it’s been so rewarding.