First, what stage of growth are you in? Early veg, late veg?
I always recommend starting off at 1/4 to 1/2 of the recommended feeding. Start low and you can add more, its way better to do it like this than to have problems because you gave too much too early.
After initial feeding, which you'll want to be below 600 when the plants young, then you can bump up the feeding measurements to give your plants more.
It's all about learning your plant and how they like to grow, eat and drink. You want them to drink a lot, but to eat a lot as well. This is how you get the most out of your plants.
By late veg growth you want PPMs to be around 1000-1400, but don't always let these numbers keep you in a mold, you can experiment with higher PPMs if, AND ONLY IF, your plants are responding well when you feed them.
Just remember, nutrients are always necessary when growing in hydro applications. You'll get a base idea of how to feed from the GH feeding chart, but it comes down to you and growing your plants as best you can.
I hope this helps, and if you have any other questions you can tag me or any other hydro guys, sometimes it takes a day or two to respond, but I'll always get back to someone if I'm tagged!