The basic principle behind EI is to always have enough of every nutrient in the tank, and rely upon a weekly 50% water change to get rid of any excess from dosing too much. I have the same size tank as you, and I dose 1/4 to 3/8 tsp KNO3 three times a week, 1/16 tsp KH2PO4 three times a week, and traces on the days I'm not dosing the macros. I can tell you for sure that you have to have CO2, and keep it at 30+ppm during every day or you will get lots of algae - I have learned that by experience. I upped my dosage of KNO3 from 1/4 to 3/8 tsp for that reason too - the more light you have, the faster the ferts get used up. No testing is needed, other than PH and KH if you really follow the EI principles.