Thanks very much for the advice.

The treatments I used were Tetrapond and Interpet from my local
aquatics pet shop, the non-chemical anti-blanket weed treatment used
bacteria or enzymes or something, I can't remember to be honest, but it
was recommended to me.
The pond is less than a year and a half old, but the plants and a few
of the fish were transferred from a fairly mature pond at my previous
house.

I forgot to mention that I added 6Kg of salt to my 4400 litre pond, I
believe this will improve the buffering as well as helping the fish
directly....?

The fish seem a bit better these last few days (4 shubunkins and 4 orfe
left), they seem livlier and are eating pretty well, hopefully this will
continue.

I'll have a look around on the internet for the products you suggest,
does anyone have a favourite reliable supplier?

Thanks again!


--
marmot