[Rich]

I use Star-Tron also, all year with every fill up.

I remember seeing a note from them that it is compatible with other additives, but I can't find a 'FAQ' on their new website.
http://www.starbrite.com/startron

But there is a left over FAQ on their old web site here:
http://www.starbrite.co.za/faq.html

I'd like to use Star Tron when I fill up the tank, but having used other additives before I'd like to know if Star Tron is compatible

Star tron is compatible to any kind of additives you have used previously without any danger.