PPM's vs. Feeding directions

So I want to make the transition from soil to coco mostly because i'm getting bored and want to try different stuff. In the past I've used fox farms ocean forest mixed with a bunch of perlite and I've fed mainly with jacks classic all purpose and bloom booster. Everyone says feed at half the dosage so that's what I've been doing and I've had pretty good results. I've battled with a few deficiencies/lockout issues but they were minor and I found the soil to be very fogiving. I've never had a ph meter, I've just used the drop tester and would get it pretty close to where I wanted (I dont mind if the PH drifts a little)
and I never had a ppm meter because again I just fed at about half the recommended dosage.

Here's the thing...In preparation for my switch to coco I got a ppm and ph meter and calibration solution for both and I was curious to see at what level I've been feeding so far. My tap water right from the faucet is around 150...when I add the amount of nutes that I normally do (jacks classic all purpose and bloom booster) my ppm's only raise to about 270 and when I use full recommended dosage the ppm's are still only around 535 for the bloom booster and 390 for the 20-20-20.
I keep reading that in late veg and flower my solution should be anywhere from 900 to 1200 so does that mean I have to use 3 times the amount of nutes suggested?! I mean I dont mind since jacks is relatively inexpensive and seems to work pretty well. Then I started thinking how I've gotten away with under feeding all of this time and figured the fox farms soil must've made up the difference. But that's just a guess. So my question is should I be following the directions on the label or my ppm meter? Putting almost a tablespoon of nutes into a gallon of water kinda freaks me out.

Side question: If I transplant a plant from a 3 gallon container filled with fox farms into a 5 gallon with coco would that be a bad idea? Where should my ph be in that situation? I'm thinking around 6.5 ish? the same as if it were all soil?

Any advice or help greatly appreciated

Question the PPM conversion accuracy, EC with pen should be more accurate as this is pretty similar between equipment mfg.
I am in the water treatment business and unless testing for ONE additive (say a blended phosphate) I would use EC as a test for nutes.
Got this from another site -

"if you want accuracy then forget PPM. The measurements are in made in EC and then converted to PPM by a mathematical equation. EC measures anything in the water, period. 0 EC water is pure H2O, a perfect insulator. If it has anything in it at all it will conduct electricity and show up on an EC meter. How sensative(How many decimals) the meter is depends on how much money you have. The more sensative the meter is the more money it will cost"

Plus different meters convert by different formulas????? one .05 another .07 stupid that there is not a standard for this but it is the way it is.