Damn man your setup is insane. you prolly have one the best setups a person could ask for.

You should be able to go a few weeks without feeding them were you got the pro-mix but if your going to use synthetic fertilizer. I would recommend an Ec/ppm meter, It'll let you measure the mix in the water before you feed your plants with it. It does not work with organic fertilizer though it will only read an pick up what the plant has available.