Most plants are loaded with fruit, so now is an important time to keep up with the high potash feed, once a week is fine in the soil. However, if you are growing in grown bags then a little more feeding is required as there is less reserve.
If your plants seem to be struggling and going thin at the head, then a booster high nitrogen feed would be better for a while.
We had had quite a lot of damp weather lately, so it is very important to keep a good air circulation. Firstly by removing some lower leaves, and secondly by leaving the doors and vents permanently open, except in strong winds. This will help keep some diseases away, or at least stop them starting too early.
Do not worry that your plants will be a little colder at night at this time of the year, because with higher humidity about, it is better for them to be a little colder than encourage mildew.
Splitting fruit is caused by over watering or uneven watering, too much at one time.
BLOSSOM END ROT (BER)
This is a deficiency, usually calcium or a chemical imbalance. But it it more often a simple matter of under-watering. Once the damage has been done to some fruit on the plant, there is not a lot you can do about that fruit. Just rectify your watering should resolve the problem, but you will still get the pre-damaged fruit maturing, so don't panic.
There is a whole section about blight on on my blog, just be aware of any of your potato plants, which is where it can start from. You should always plant potatoes as far away as possible from the greenhouse or outdoor tomatoes. Also beware when handling potatoes, always wash your hands before touching your tomato plants. Just basic hygiene rules, but it could save you crop.