Flora series is a 3 part nutrients , you need to use the 3 part for an effective solution and if you wanna keep the right amount of every nutrients. The reason why you CAN'T go WITHOUT flora micro is that it's the ONLY ONE that have Calcium in it , the others have Magnesium and if they were in the same bottle it would have create some salt. So to avoid any kind of deficiency you need to use it. The only case you can use only 2 bottle is if you are using the Lucas Formula and it requires only the Micro and the Bloom , the proportions are simple , in veg : 4ml of Micro and 8ml of bloom per Gallon of water ; in bloom you double up: 8ml of Micro and 16ml of Bloom per gallon for a EC approximately around 1.8 and back in the times it was considered as an aggressive feeding schedule