Drop your nitrates to 10ppm and your phosphates to 0.1ppm. Keep it steady at these levels. To me, that is the sweet spot.
If nitrates rises up to 15-20 and phosphates 0.15-0.2, I would consider that high already...and work to bring it down.
And you need to adjust your dosing based on ICP if you don't want to do water change. Personally, I would do a large water change, and let the tank settle for a day or 2, then send in an ICP as 1st baseline. Keep everything the same (like everything from trace dosing to equipment parameters and run time), and send in 2nd ICP about 1 month later. This will tell you the tank consumption of trace element. Then adjust your dosing...and send in 3rd ICP after another month to confirm dosage is correct. Then you can space out the ICP testing for longer periods.
Or just do routine water changes, and you don't have to do ICP.
Just remember that carbon dosing, UV, Ozone, carbon, skimming...they all affect certain trace elements, so it is best to lock those parameters in place before starting this series of ICP test.