3-part by GH...is a product Advanced Nutrients "copied". they are the same thing.
I actually have mixed AN, and GH 3-part...

and you do still need to measure EC/ppm, but I can tell you. If you run you seedlings at 2ml per gallon each, then in week 3 changeover to 5 ml per gallon each...for your grow, you will be within safe limits...
I would get a EC meter ASAP though, but If you follow the guideline I gave you...It is a safe zone..

PH is imperative. peace

I also want to advise everyone...that although i use botanicare products pure blend pro on all my veggies. I quit using it for pot...3-part blows it away...yield wise!

I do however still use Liquid karma, and calmag+, (botanicare)
hygrozyme.
From AN...I use BUDBLOOD/BIGBud/Overdrive & final phase

Start simple build as your knowledge grows. peace