Water or nutes ?

New to using my ppm meter,and have a couple questions. If my plants are eating between 50 and 90ppms a day am I still to lean? What's acceptable? The majority start at 700ppm or 1.4 ec ,one around 550 ppm or 1.1 ec. And I have just been adding back RO water between res changes. Should I be adding back nutes between changes? Right now I just change them when the EC gets close to half of what I started them.The plants r just about to starts 3rd week of flowering and look as healthy. As I said I am new to the ppm meter, and I also changed from GH nutes to dyna gro. With the GH nutes you could just see by the color when it was time to change out the buckets.

I started with 0,4 mS when my plants were seedlings and am giving them about 1 mS now.

I don't add any water between changes. I just let them drink about 2/3 or 3/4 of water and then change the whole res. Toping up with nutes is not a good idea as plant could be taking in much more of some element then some other element, and by adding more of both you could be increasing the concentration of unused element to toxic levels. Toping with RO water would dilute nutes way too fast.

top off with calmag'd only water >200/250ppm???