Prevention is better than cure is my method.
Yeah I think I know where they came from.
I've been recycling the same 200L or so of Canna Pro+ coco as my base stock for about 4 years now, no problems, everything spot on and the plants love recycled coco.
This time I topped it up with some cheap coco bricks from Home Bargains at £1.89 for 50L, it's had garbage in it like bits of leaf and stones and shit pressed in it when I've used it years ago so I vowed not to use cheap bricks anymore.
Stupid cunt me didn't listen to my own advice and the price swayed me, you really do 'get what you pay for' when it comes to coco and I reckon they've come from that.
It's my own fault.............