I am a water only grower also! I have been re-using my soil for over a year. I use steer manure, chicken manure, EWC, forest compost and Mushroom compost for re-amending the soil along with a few other amendments. I do make an ACCT every now and then with mushroom compost, EWC and molassas just to feed the soil. I have not adjusted the ph of my water in over a year as it comes out of the tap at 7.14.
My soil is a bit hot in the beginning so I have some dark green happening but it lightens up with time. The only issue that I have is that I forget to check on my plant's from time to time and they get too dry. Once that manure dries out it is hard to get it to soak up water again.
This is one of my current plant's. It is a Platinum Bubba at day 3 of flowering. The shiny spots you see are from the neem/spinosad spray she got a week ago when one of my other plant's had the Borg!!! My rooms run cool so I get some purple stems (65 degrees at dark and 78-80 degrees at lights on)