Where did you get your seeds? I am guessing that you are using bagseed and that is the cause of your hermies. When you find seeds in bags that should be sensimillian, they are most likely the result of the plant selfing. When this happens the hermie gene can become a dominant gene and the resulting seeds have a far greater chance of hermying, even without any kind of stress conditions. If the seeds you have vegging now came from the same source, most likely you are going to have the same problems.
If this is the case, the only real answer is starting over with quality genetics and cleaning all your spaces very well to get rid of any residual hermie pollen.