Hi Everyone
Thanks for your replies. If I'm honest I still believe it's parasites that I'm missing but god knows how for the amount of scrapes I've done. I received a number for Ritchie Bunting so I've contacted him and he was coming tonight but I've had to self isolate so hopefully he'll get over next week and find out what's happening. My air pumps are just underneath my decking where my filters are so any fumes getting into them would only be from them or any equipment in there. The only thing I could think of to do it would be the Heat source pump? but I would've thought I'd smell them myself. Thanks for all your help and I'll post an update when Ritchie has been.

Cheers

Craig