The ONLY time to put adverts on your blog is when they are useful to your visitors. If they are irrelevant and non useful, then they are just a distraction. The problem online is that just over 98% of all advertising is IGNORED by people. With 2,300 uniques per month there are much better ways you can monetise your blog than advertising. For instance – zero advertising but membership, where your members get more in depth content than the free visitors.