Jasper wrote:

Every morning I have to clean the pump's filter as it's completely clogged
up with sludge and the water has stopped flowing. I clean it with water
from my water butt rather than tap water. I also empty all the water out
of the bio filter into a container and the following morning after the
sludge has settled to the bottom, I siphon the clean water back into the
pond.

The first 4 or 5 days I had to clean the pump's filter twice a day so at
least there is some improvement there,
....
Am I doing the right things so far?

Vacuuming the bottom would probably help, in the long run. In the short
term, it might stir up even more sludge and clog up your filter again.

The fact that it's so easy to clean out your filter suggests to me that it's
really undersized for your pond. Otherwise, yes it sounds like you're
doing the right thing. You don't want to make massive changes quickly if
the fish seem healthy now.
--
derek