Thanks for that

Your enthusiasm is catching
I won't be able to soak the soil for two weeks - I have nowhere to put the fish

so I'm going to have to put them in and keep my fingers crossed

but DW does mention leaving the soil out overnight to gass off any ammonia - now that I can do

I'll be sifting out the big stuff anyway.
I was also thinking of putting cleaning from the filter into the soil layer too - would this help do you think?
I'll have one last look today for the MiracleGro Organic Choice that I've seen mentioned, someone in the UK must be selling it as it's available online and if I can't find it then I'll get the Arthur Bower's one. I've been reading Westland is a bit useless so it's going in the garden tubs.