The treatment you need is called Rot Stop and is available everywhere, this time of year. It is a foliar spray. IMO, it tends to attack indeterminates, mostly.
Last summer, I had some orphan plants and broken off stems early on and so, I potted them. In the heat of early summer, I had to water too much. Then came rain. Then came blossom end rot. I had nothing, just picked off the bad fruit and since the weather co-operated, the rest were just fine.
This year, I am testing out several miniature/dwarf plants. Even with 3” of rain in 2 days, much misting needed prior to that because of sun, low humidity, NONE of my miniatures had rot and are doing well, so far. The presently bearing ones were started inside in March.
One new (to me) cultivar was named Silvery Fern. It was described as very cold tolerant, would set fruit in 58 degrees and was early at 60 days. Supposed to be a Siberian variety.
It needs a LOT of water! It would be drooping every afternoon. It is also rather a strange plant in that it is doing terrific in a smaller pot (10 inches) and is a sprawling mess in a larger (12”) one. The pot-bound one has large fruit. The one in the larger pot has very small fruit. Both were started indoors in April. This morning, after another 2” rain last night, I found end rot on one fruit of the pot-bound plant. I pulled it off and applied Rot Stop. It is cloudy today, so no need to worry about leaf burn. Otherwise, I would have applied it late after sundown. Also, excess nitrogen can facilitate the calcium deficiency, so hold off on the fertilizer or make weaker solutions and apply less at greater intervals.
Best potted plants this year: Patio Princess hybrid (2”-3” tomatoes) and Red Robin, a miniature with cherry tomatoes. Patio has an earthy flavor, while Red Robin is quite tart and bright. Seeds for all these and the Silvery fern are available at ContainerSeed.com. They ship slow, so be prepared to wait.
My garden plants have more foliage than I have ever seen!! However, I only have small greenies, so far and I planted out 40 days ago. I hope I have enough time left (9 weeks, max) for harvest. I am pretty sure I will be digging up my peppers and finishing them inside in 12” pots. It has just been too cool, too cloudy, too many days with high winds and it seems when I finally give up on the forecast and water the garden, it pours the next day. Sweet corn is stunted. I planted early varieties of everything this year, except the Big Mama Romas and it isn’t really helping.
Sounds like a burger chain in Philadelphia.