I had thought that by now another forum member would have explained another reason for BER. Many folks have BER but the reason is different in their case. That reason is irregular watering and by this I mean the plant gets too much water for a time and then it gets too little water for a time. I suppose this may be your case as container gardening is a little different than in ground gardening in that it is easier to water too often and not maintain a proper moisture level in the soil. I don't know of anything except epsom salts and/or proper watering that can control BER. IMO, I think that the two are unrelated except for the destruction of the fruit. I have yet to understand what irregular watering as to do with fruit growth except that the young fruit intakes so much water it cannot grow fast enough to "rid" itself of the excess water. BER can affect all tomato fruit but it mainly shows up on newer fruits. On older fruits cracking occurs when too much water is applied at one or two times but BER can occur.
In a perfect tomato growing season I must use epsom salts or I will get few tomatoes. On some varieties none at all. If I have a season where it rains a lot, dries out some and then rains again and dries out some I will have some fruits that will have BER or what looks like BER. I am not 100% sure that the two are the same thing although the results are identical.
