Yeah, -2 tbsp per gallon is good for the soil microbes and beneficials, and during flowering it adds a carbohydrate boost and potassium. Both are vital to healthy bud production.
The blackstrap is the best and can be found at wal=mart & loew's lawn and garden dep. I also found it in a pelletised form at a feed store up the road.
I've read that in some cases it can increase bud size and density by up to 30%.
Party On!