I don't know about a drench.....I feed from a 2 gallon watering can. In that I added my usual nutes and then 1/4 tsp of GoGnats, thats it. Ph'd and went on with biz.
That was about 1.5-2 weeks ago and since then I've up'd to just about 1 full tsp per 2 gallons. Then i feed as normal.
As...