If the tap is really 20ppm of NO3, (N-NO3, or just NO3?), then I'd cut the KNO3 by 1/2 or so.
Add K2SO4 in place and perhaps a little MgSO4, epsom salt in place of the Gh booster. So mix these two together and dose after a water change, say 1/10th MgSO4 and 9/10th's by volume K2SO4.
I'd suggest using Fe DTPA in conjunction with CMS+B for the dosing
Say 1/4 DTPA with 3/4CMS+B.
As far as a solution, the only "rule" is not mixing together Fe traces with KH2PO4, the PO4.
So say you want a solution that will last 2 weeks:
Add the total volumes listed for 2 weeks into a bottle and fill with 500mls or 1 liters, whatever amount you select. Then divide the mls by the 2 weeks, or whatever time frame you want to make, so 500mls/14 days in 2 weeks.
35mls per day etc.
This is just an example.
As far as a dosing of daily using a richer PMDD+PO4 method:
Should address most questions, you can also find conversions for table and teaspoons to grams.