I have always cloned with rockwool and I use a few different things when soaking the stuff. First I use some Hydroguard (I think like 10ml/liter of water) to make sure no algae or fungus or anything starts growing in my humidity dome. I also use 3ml/liter of Nutri+ START 0-1-0. I usually mix them seperately and pour two liters over the rockwool and let it soak overnight. Then the next day I pour/drain any extra sitting water and cut clones and plop 'em in. No gel, no powders, and 80-90% start rooting in 4 or 5 days and have tons of roots bursting out of the rockwool cubes by like 10 days. If you are dead-set on using powder or gel you can probably just just soak in ph'ed water and, like the guy above me said, a couple drops of bloom nutes
Good luck cloning bro and peace RIU!
