Firstly you will need permision from the DDAF for a drain down and they may require a health check on the fish. What ever you do, Do not neglect to contact the DDAF.
I have owned and run a fishery in France for over 10 years in the SW France and needles to say seen a lot of fisherys come and go, But one of the biggest reasons of seeing fisherys going to the wall is P ing off the DDAF.
Fatfish is very clued up and knows what he is talking about.
Tight Lines
Paul