Hey DW
As above, sounds like your soil has some added nutes so maybe you can get away without using your own. It usually says how long the food will last on the soil packaging. Remember that if it says 6 weeks and you cut the soil 50/50 with perlite then you'll only get around 3 weeks with it.
I just mixed up some of those GH nutes so I took some notes for you. US gallons are different to UK gallons so I used litres to make sure we are talking about the same thing.
My water was 45ppm and ph7.0 when I started.
1ml FloraNova veg nutes in 1 litre of water = 610ppm at ph4.0
1ml FloraNova bloom nutes in 1 litre of water = 620ppm at ph4.0
If you aren't used to ppm and you are in soil then a rough guide would be 800-1000ppm is full strength and should only be used on mature plants and 1/4 strength or 200-250 should be fine for the young guns.
A ph of 4.0 is a bit low so I use a little PH UP to take it to about ph6.