I do my best to reply to all the comments. I am happy to share with you how I fertilize the water. I use 12 grams of Master Blend fertilizer for hydroponics, 12 grams of Calcium Citrate, and 6 grams of Epsom Salt for every 5 gallons of water. I just fill the tub with water almost to the top after mixing the fertilizer into the water. Then I put the raft on top with the seedlings. They grow on like that until harvest. It is very easy. Here is a link to a post I did last year on my process.

@sunscape/hydroponic-experiment-with-lettuce-by-sunscape