I use a weak 20-20-20 fert for veg. (designed to be mixed with water, no solid granulars)...and a weak 10-52-10 fert for flower.

but, most growers prefer 10-5-5 for veg...10-30-10 for flower. What ever you use...it should mix VERY well with water and keep it on the WEAK side. Better underfed than overfed. IMO.

What is the MG tomato fert ratios?...does it mix well with water?