Thanks Gus, I don't know why I put bacteria, I know it's a fungus. * Guess it was a bit early in the morning!
We have our media tested regularly to ensure the Trichoderma is there and active. *Drenching with any fungicide we have used kills it stone dead but spraying or misting the plants usually just suppresses it, it comes back.
I believe the pH of the media is also quite crucial to healthy Trichoderma colonies.
P.S. Have finally sorted out some T-shirts!