GH Booster adds minerals back to the water that you normally lose through water changes...my GH is 3 and I still use seachem Equilibrium to raise it to 8 or so.
For traces, I use CSM+B , I dose Seachem Iron on days I dose micros and lately have been adding Magnesium sulphate, ( Epsom salt) in the same amount as CSM+B.
Great results as far as growth and color in all my plants.
I have a 17G tank, and I dose the dosage for 20-40G tank, I even dose extra PO4 because I was getting some GSA...
I think I'm about to increase to even bigger amount of ferts because plants grow like weeds..
So you really have to play with them and find the sweet spot.
And dont forget to add your ferts back after water changes otherwise you will run into algae problems.