Since the tomatoes are blooming, I want to try calcium supplement to prevent blossom end tot. That happens mainly with sauce tomatoes. I really don't know if it helps. Internet sites are all over the place on that, as is research on google scholar. It seems like the bottom line is, they just don't know and have not really done the work - spray some and don't spray others, and see what happens, and report on it. Some sites say, absolutely, use the calcium. Others say it's useless. The joke is on me since I didn't think of that until I sprayed them all.
The instructions say, spray in early am or evening, during periods of rapid growth. Spray to point of run-off. Apply every 5 to 7 days. It's just calcium chloride so I don't think it will hurt anything. For the rest of the sprays, I'll spray all but one of the hybrid Romas and also leave a nonhybrid Roma unsprayed to see if there is a difference.