dude, bust out your google, n search "Hydroponic store in (your city n state here)". It will show you the nearest hydro shop around.
DO NOT USE MG NUTES FOR YOUR PRETTY FUCKIN PLANT BRO. i dont wanna see your leaves get burnt. i mean MG is alright in some cases, but to be honest, Mg leads down one common road for the most part, and its nutrient burn. Alot of people have had successful grows with Mg, but it takes ALOT of effort and patience to do this. If your already using MG soil, dont bother with the nutes.
Now, back to the hydro shop. If you find one within 30 miles, its worth the drive. What you wanna do, is go grab yourself a small bag of Fox Farm Ocean Forest soil mix. Its organic, and your plant will fuckin love it. If your gonna do it, do it now, cuz in another week or two it will be too dangerous to transplant your shit. But if you cant or dont wanna transplant, just pick up some FF big bloom and tiger bloom from the hydro shop. N if you need some advice on how to deal with MG soil and FF nutes (im just assuming your using MG soil, cuz thats what everyones parent has layin around, and usually if you live with them, that what you end up using, cuz its free, lol) , you just ask your hydro shop pro. Tell him your growing some tomato, cucumber, and pepper plants, and you need to know if the Fox Farm nutes will burn your veggies if your using Mg soil already.
Now, the feeding. Your gonna want to give your plant nutrients somethin like once every other feeding for the first couple weeks of flowering, and then as they resin and bud production gets more and more involved, i would move it to every feeding. You shouldnt change how often you feed your plants water, just do that as usual, but add nutrients to the water you feed them. Should be somethin like once every 2-3 days.
Bah, im just ramblin on now, take from it what you will. I hope i helped out a LITTLE bit at least, lol.