Honestly. I suggest getting a PPM Meter. Without one you are playing chemist.
It can be done but it's only $20-$30 for meter.
That is going to put you exactly where you need to be and you will have alot more of an understanding of what's going on.
Even after adding these mixes if my PPM is not where I want it I adjust the nutes/water.
During the first couple weeks of veg I add approx. 2-4 mL of Sensi A & B per Litre of water in the rez.
My rez this grow is an 18 L sport cooler. 15 L of water in there so 30-40 mL of A and 30-40 mL of B.
Then follow the directions on the back of the Voo Doo bottle. 2 mL per L during wks 1-2 of veg & flower.
During weeks 2-4 of flower I add 2 mL per L of Big Bud liquid to the rez. During wks 6-8 I add 2 mL per L of Overdrive.
That's a small rez you're working with there. But 1.5 gallons is equivalent to 5.6 Litres.
So with the Sensi A & B, I would add 8-10 mL of A, 8-10 mL of B, & 8-10 mL of Voo Doo (VD only during weeks 1&2 of veg & flower).
But knowing the exact PPM will be alot more beneficial to you to know.
Enough with my rambling.. Lol!