Not sure on the ppms. But DO NOT add more Gravity. If you do, you can likely kiss your plants good bye!! Gravity runs hot hot hot!!! There's lot's of articles on here about it. Do a search and see for yourself.
That said, I run Gravity in my DWC system. I run it at 1/3rd the recommended strength along with gen hydro flora nova series, Dutch masters zone, gh liquid koolbloom, and fox farm cha. Ching. I keep my ppms always under 800 max and usually closer to 600 ppm. I rock the 5.8 ph and have had incredible results.
Hope this helps