How do you fix blossum end rot on tomatoes?

I've read other answers and not sure what to do. This bottom rot has been happening on the green tomatoes and when they start to ripen it gets even worst. The leaves on the plants are curled too. Thought is was because of the temp change 3 weeks ago but they are still curled.

One answer says they need more water due to lack of calcium. How often should you water tomatoes? Everyday? Or when the soil is dry an inch from the surface? Is there a calcium additive I can add? More or less Miracle grow?

This is happening on the full size tomatoes. On the red cherry and the yellow cherry tomatoes they are just fine.

Not sure what to do. Any information would be great. Location is in Grass Valley, CA. USA.
Thanks

Answers:
i have had the problem and it was due to overwatering.

Other answers:
The very best way is to get the blossom end rot spray from the store. We have used it quite a few times, does a PERFECT job.
The very best way is to get the blossom end rot spray from the store. We have used it quite a few times, does a PERFECT job.
I would think your over watering them...where are they in relation to the srinkler? I haven't watered my tomaotes for a week...the ground is rock hard but they are thriving. Once it starts its hard to stop...get somemore plants and try again..it's not too late. I live 40 west of St.Louis......
This could be caused by a blight or fungus. Often times when you water tomatoes and soil splashes up on the lower leaves it causes the plants to develop blight or fungus. It starts out as yellow and brown spots on the leaves and as it advances it causes the leaves to curl and fall off generally starting at the base of the plant. Eventually it can affect the fruit. Check with your local garden center and they may be able to suggest a good fungicide.
It's usually caused by uneven watering. Pick a regular schedule, like on Tuesdays, or on Tuesdays and Saturdays and stick with it.
This is a calcium deficiency problem. I use Green Light"s blossom-end rot spray. It can be used on cucumbers, melons, and peppers. Be sure to apply it early in the morning or late at night other wise the foliage will burn from the high temperatures. It works for me.
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