Reducing acidity in Northern Indian Cuisine (chana masala) I have been buying various spice mixes to make Pakistani/North Indian food myself. My issue is that in dishes with yoghurt and/or tomatoes, the end result always winds up being too sour. It happens with my karahis and also, most annoyingly, with channa masala.
I have tried various kinds of yoghurts, including plain low-fat yoghurt but also a Turkish one I found which had 10% fat. The result didn't change much. So, I don't think the type of yoghurt I am using is the problem.
Other than the acidity these dishes turn out alright. Which steps can I take to reduce the acidity of my dishes?

Update
I am restricting this question to chana masalas since that's what I have played around with the most. However, I am open for more general answers as well.
I usually put about half the amount of onion as tomatoes. Other than that, I usually follow the recipe on the box. The one I am currently using is this one.
Perhaps you could try using a smaller kind of tomato, like cherry tomatoes.
These are usually much sweeter in my experience and in general have a lot more to offer in terms of taste, compared to large tomatoes.
A mixture of both would also work if you don't have enough small tomatos at hand, since the sweetness of the cherry tomatoes will counteract the acidity of the larger ones.
If smaller tomatoes aren't an option, I would also go for high quality canned ones, as other people have suggested.