Bloosom end rot on some tomatoes
John I
Posts: 4
My best tomato in the g/h this year is a Moneymaker which is now full size & has over 100 fruits & flowers on! Planted in a 10L pot with a mix of compost & John Innes #3 with gravel on top. Annoyed to find yesterday among the fruits just beginning to change colour, 10 with blossom end rot. I have since removed the affected & watered the plant with a bit of BiCarb, Lime & Wood Ash, (not all at once & notalot!). The rest seem OK, my other Tomato plants are Gardeners Delight in Levington GrowBags & don't seem to be affected.
My question is - do you think the lack of any significant KH or carbonate hardness in our tap water has contributed to this situation?
As a keeper of Koi for almost 40 years I do have good water managment skills, as any Koi keeper will tell you - look after the water & the fish look after themselves 
Testing of the water supply has regularly shown a KH of between Zero & One, therefore I have to use BiCarbonate of Soda added to my pond water when topping up to maintain a buffer for the PH, not to mention food for the filter bacteria.
This is the first time I have considered the fact that the lack of calcium is perhaps primarily down to the mains water I feed the plants with.
Cheers, John
Posts
I've always found Italophile's posts on tomatoes really helpful - in this thread from last year he explains the causes of BER http://www.gardenersworld.com/forum/problem-solving/tomatoe-problem/86841.html
Hope that's helpful
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
Thanks Dove but that doesn't address my question at all
John
It may not address your question re the hardness or not of your water supply, but it does address the root 
of the problem which is the BER affecting your tomato plant
As I understand it, and as Italophile explains, it's not the lack of calcium in the water/soil that's the problem - it's the plant's inability to access and distribute it throughout the plant, due to stress.
I know many many gardeners whose tomatoes are watered solely with rainwater from waterbutts, which would surely have a very low calcium content, and yet they regularly produce prizewinning tomatoes for the showbench.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
John, regardless of the water, the mix in the pot is good quality and there should be suffifcient calcium available to the plant. Has the plant been fed? If so, all decent tomato fertilisers contain calcium.
If your other plants are BER-free and in the same or similar mixes, and have been fed, the water isn't the problem.
BER is about the most frustrating tomato problem. I found one infected tom on one of my plants last night. The plant is one of 16 that enjoy absolutely identical growing conditions. One infected fruit out of about 100 toms across the plants, and the infected fruit is the single, solitary sufferer amongst about 10 toms on that plant.
Irregular watering is believed to be one of the causes of plant stress but there can be others - strong winds, fluctuating temperatures, extreme temperatures; anything that can upset a plant's equilibrium.
And, sometimes, as in my case, there seems to be no explanation.
I had this problem until I began putting egg shells around the plants. It helps keep slugs off to.