I like Fox Farms, it's 6-4-4 for the Grow Big(vegetative fert). Main thing is whatever you get, make sure the N is higher for the beginning and P is higher for when you switch the lights to 12 hrs on & 12 off, as well as don't start off with as high a dose as your fertilizer recommends-try half dosage every other watering. Once you get to know the plants and their requirements you can go higher but most newbies end up feeding too much and hurting the plants and their yields, I know I did.

If you have a hydroponics or indoor gardening store around you, go browse and maybe ask a few questions like what they recommend or have used. There should be no need to say what you're growing, you can say something like tomatoes, houseplants, or annuals if they do ask though. If there's a hydro store around, they will automatically assume it's weed in my experience but they're cool as long as you don't specifically mention it in their store (my idiot friend got kicked out when he said something about bud in front of another customer).