Those of us who are pretty new to high light planted tanks can do a lot better with fertilizing if we use the EI method for fertilizing. That means dosing about 5 to 7 ppm of NO3, about a tenth of that of PO4, and whatever K comes with the first two, three times a week and dosing traces on the other days. Then changing at least 50% of the water once a week to make sure none of those elements build up too much in the water. No testing, unless it is to determine how much CO2 is in the water, whether the KH is high enough to avoid pH crash if dosing CO2, and GH to make sure our tap water has enough Ca and Mg in it. CO2 can be added in as great an amount as the fish are comfortable with, and should be to have an optimum amount, but must not be allowed to fluctuate much from day to day (night time doesn't matter.) When we try testing for nutrients we are always at the mercy of the accuracy of the test kits, which is very poor for hobby grade kits. Once we (I include myself) become more experienced, then might be a good time to try to fine tune fertilizing by doing testing and dosing.