Will this work for my 45g

Your tank is about the same size as mine. I mix 3/5 tsp of KNO3, 1 tsp KH2PO4 into 16 ounces of waterr, and dose one ounce per day. That makes my dosage 3.5/16th tsp per day of KNO3, about twice as much as yours. My KN2PO4 would be about 1/16 tsp per day, also about twice as much as yours. I have only 55 watts of AH Supply PC light over the tank, but raised about 6 inches above the tank. EI is a very rough estimate of how much to dose, so if you dose twice as much or half as much, either could be right, depending on how many plants you have and how fast they grow.

That is why EI is such a great system - no need to get exercised over the exact amounts of anything. This is because Tom has found that having too much of any fertilizer, within reason, will not cause any harm. And, the water changes reset the tank every week.