Prior to running ZEOVit in my system my Nitrates sat around 15 to 20. If everything is doing well and you are happy with the colour and growth I see no reason to do anything.
How deep is your sand now?
I'm fearful of the debates that will start with the DSB, shallow SB or Bare bottom if too many varied opinions are given on this topic
Many are now finding that the problems outweigh the solutions when running a DSB.
do you have room to add a section to your sump (if you have one) for a refugium?