No, powdered milk won't help.

No, you don't need to buy anything.

All you need to do is figure out out to maintain an even moisture level in the soil/potting mix.

Tomatoes in pots are quite susceptible because of the limited root space. They dry out rapidly.

Some tomatoes, such as Romas, are very susceptible to blossom end rot (BER).

Are you growing in the ground or in containers?

Thanks in the ground

I water em all the time. Every day. We are in a drought and they get a lot a city water with who knows whats in it? Maybe that is the problem. I always heard lack of vitamin D produces the rot on the ends of tomatoes?

Plants in the ground don't need water every day, even in the hottest areas.

Common mistakes with people who water every day is that they water too shallowly, which causes a lot of fluctuation in moisture and stimulates the plant to grow a shallow root system close to the surface. This makes it more susceptible to water and temperature fluctuations.

City water has nothing to do with it.

They need slow, deep watering that gets way down into the deeper levels of the soil. This stimulates tomatoes to send their roots deep down into the soil. Because the soil down there is more resistant to temperature and moisture fluctuations, the plants are more resilient. How often? Nature has no schedule. Dig down a few inches in your tomato bed. Still moist down there? Don't water. Dry? Water well and deeply, making sure the water is soaking down into the plant's root zone and not running off. You eventually develop an instinct for when you need to water and how much. Until then, use your fingers. They're a cheap, reliable moisture meter.

The "conventional wisdom" is that BER is a lack of calcium. The conventional wisdom is mostly wrong. If your soil is calcium deficient, yes, that can cause BER. But ground soil is almost never calcium deficient. The issue is that calcium is hard to transport, and a stressed plant, especially one getting too much or too little water, can't move the calcium within its tissues all the way up to the developing fruit. Extreme temperatures also contribute, as they affect water circulation in the plant, which affects the transport of calcium to developing fruit. Younger plants with smaller root systems also tend to be more susceptible to BER. Weeks later, the problem caused by these things shows up as BER in the fruit.

Lots of calcium products promise to fix your BER. They're mostly bunk. By the time you see the BER, the conditions that caused it are weeks in the past. You apply these products and the BER appears to magically disappear, but what is usually really happening is that the problem that caused the BER resolved itself, and the new fruit that set since didn't have the problem.

One exception is if you're growing in containers in a potting medium that doesn't include lime or some other readily available source of calcium. In that case, you'll need to make sure you fertilize regularly and that the fertilizer includes a form of calcium available to the plant. Most tomato-specific fertilizers do include calcium and other necessary minerals. So no need for fancy anti-BER sprays or solutions. Just get a decent fertilizer and make sure your watering is consistent.

Re: watering--tomatoes are very Goldilocks about both temperature and moisture. They like things to be just right and don't do well with too little or too much. When their roots are waterlogged, they don't function well, and the plant suffers. If they don't get enough water, they're prone to drought stress. Both conditions can lead to BER.

well I don't have too much water. We are in a moderate drought of 3 months. I water em and have em mulched and soil around them covered but guess not watered deep. Will have to try that. thanks