Thanks Bill. I had read that forum a while back but haven't really nutted out the solution (shooting two types of data, with and without filter). At least that explains the lack of yellow star colour
I think I'll just do a session without the filter once the moon goes away and work with a greater number of shorter subs. With the filter under lots of LP I can get a nice 5 minute sub so might drop back to half that without it. Or get down to a dark site...