1st Grow, using FoxFarm OF Happy Frog. Need Advice on nutrients. When to start? what nutes to use? Schedule?

4-8 weeks? watch lower leaves for any paling... that's probably the first thing you'll need. slowly ramp up concentration after that. i wouldn't go full dose based on what FF says in instructions. what you need will depend on how often you apply it -- every other irrigation? every third? make sure you don't leave dry pockets when irrigating. you don't need runoff with soil, but a little bit ensures the entire thing got wet. you can dial in volume to reduce that waste as you go. when you start fertilizing at full doses, a littel runoff is probably a good thing. no longer wasting what was amended in the soil, but the runoff will help maintain what you added at a consistent concentration. it's impossible to know exact contents of that soil. so what you need and when is like riding a bike.. you just have to experience it and go with the flow. watch for hint of deficiency. take note of how long that took, and pre-empt it next time. slowly ramp up dose.. observe and react. you may need a fuller compliment of fertilizers as time goes.