I prefer Amazon when it comes to Jacks. Their shipping is discreet as long as the item is Prime eligible, meaning Amazon ships it to you, not a 3rd party. The Cal-Nit I use is $10 for 2lbs, 5buckethydro brand. I also use fulvic acid at .40 grams per gallon sourced from customhydronutrients, and yes they have discreet shipping.
I currently grow ebb & flow style on a flood table. Flood every 3 hours. I primarily use hydroton but I've used coco a lot too in the past. When it comes to the Jacks 321 formula I've found that 3.6 | 2.4 | 1.2 gives me the best results from start to finish. I start with clean RO water, about 10 PPM's, but I like to add about 10% tap water into my res to help buffer.
I've found that when I'd dilute the PPM's down to say the 600's, that there wouldn't be enough calcium available in the water. Since I've bumped the PPM's to around 1000 to 1100 the plants have responded well. This includes seedlings, veg, and flower.
Here's a shot of the flower tent today. The grapefruit is a bit pissed off because I leaf stripped her a few days ago.