Blossom end rot in desert soil
I get blossom end rot in my tomatoes, peppers(even worse), and a little in squash. Water/soil moisture isn't a problem. The soil and tap water is loaded with calcium but isn't available to the plants for some reason. Soil is alkaline but not horribly so.
Does adding sulfur to acidify the soil help? I have used Epsom salts which helped some.
We add acid to our water or use rain water when mixing roundup. Is this a related issue?