As far as I am aware the PST ‘rust’ problem only occurs on the main objective lens and not elsewhere. Since you mention that your objective is ‘blue’ then this would indicate you do not have the rust problem. Even with low activity in hydrogen alpha, such as at the moment, you will always be able to see the chromospheric network that occurs all over the disk – see for example the second image (right hand side) on page http://www.petermeadows.com/astroimaging/ (this Ha image was taken with a PST).
You should slowly adjust the etalon ring and always ensure you have good focus until you see the network. You may need to move the etalon back and forth and few times. If the solar disk is uniform without any texture than you are either off frequency or there is a problem with the etalon.
With your PST did you every see any prominences/filaments etc? Is it still under warranty?
Hope this helps.