I'm the only one here with any real experience with that sort of issue, so we don't really support commercial pool operations.

In your situation, there are multiple possible problems. The most likely solution is to simply replace the complete tube set, including the injector fitting and peristaltic tube. I'm sure it could be done more directly, but without being there, I'm not ready to try to walk through the process with you.

Here's a parts company online: http://stennerpumpparts.com/

And Stenner's site: http://stenner.com/
This may be the manual you need: http://stenner.com/download/IMCL.pdf

If you want to rebuilt the injector and the pump bit by bit, till you get things working, you can use those sites to do so.

Good luck.