Now I get ya. Sounds like you mix is pretty good but may be a bit acidic by the end of the grow. Cow manure as it decomposes will lower a mediums pH. You certainly want to use some dolomite lime in your mix to help maintain a good pH. Worm castings are also a growers best friend, natural slow release fert for your plants. And they contain a whole treasure of bennies for your soil. Which will help turn that cow poo it high octane food for your plants. And dont worry about the FF trio, Grow Big is the only one you need start too finish. Or go to Home Depot or the like and get a bag of Espoma Plant-Tone, what I am using this grow and it will treat you right from start too finish. Premixed in the medium, used as a top dressing or for brewing teas its hard to beat. The biggest thing to remember is green, healthy plants with lots of foliage produce the best buds hands down. A lot of what you read on these cannabis forums is very counterproductive despite the claims. K.I.S.S=keep it stupid simple and you will probably be amazed at your results.
One thing that I think is most over looked on our indoor grows is environment. One of the toughest things to get tuned in. And one of the main reasons between success and so so results. I like 80-85 lights on temps and 65 or so lights off. This simple difference between the 2 are what I consider a main key to my success. Learning to read your plants instead of a bunch of meters is also key. This really cannot be taught, just something that comes with trial and error in your own garden. Once it starts clicking the possibilities are endless...