its my first grow. I have 4 plants in a rubbermaid dish tub. my res.is a large twenty gallon tub underneath the tub. my lights are 150 mh 70hps about 10inches above the plants. they are going along fine on st8 water. should i add nutes? what should i add?

what you should do is read.

how old are your plants? how big are they? if they are seedlings you don't need to give them any nutes. but as they get bigger you you'll need to. Get some hydroponic nutes
I am using General Hydroponic FloraMicro, and FloraBloom.

Start off using a WEAK solution, and as you see how your plants respond adjust accordingly. General Hydroponic has a chart which you can find, it provides a good baseline for nute schedguling. search for it.