Reddit reviews Zatarains Pre-Seasoned Crab and Shrimp Boil 72 Ounce (Pack of 2)

You are way light on the spices, from my experience.

For seasoning 6 gallons of water you need the 72 ounce jar of Zatarains. Thats 4.5 pounds of seasoning, which is about right for 6 gallons. I would suggest adding a cup of powdered celery to the water, and also 2-3 tablespoons of liquid Zatarains seasoning. The liquid seasoning is very potent, dont get it anywhere near your eyes, I speak from experience. Wash your hands after you use it, even if you think you didnt get any on your hands.

Also in the water you need citrus. Get some lemons and oranges, maybe 3 large of each. Cut them in half, squeeze them into the water and then throw them in. That will add some zest to the seasoning and help the seasoning work better.

Edit: for additional flavor, throw in a couple of large onions sliced in half through the middle so the stem and root hold them together. You can also get some heads of garlic, peel them and throw them in there. The cloves of garlic taste wonderful after the boiling if you like garlic.