Dirty Pond. Newbie Pondkeeper.

I have just moved into a new house where there is an (approx) 4500 litre
pond which is filthy dirty and is full of algae. There does seem to be quite
a lot of goldfish in there, although it's impossible to count them as they
are only just visible when they come to the surface for food. There are a
couple of water lilies and loads of oxygenators in there. About a week and a
half ago I bought a bio filter after reading advice in this newsgroup and
just want to share with you what I'm doing for your comments.

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, although there isn't any noticeable
difference in visability! I have placed the pump on the shelf which is about
a foot deep because if I put it on the bottom it only takes about an hour to
clog up and stop the water flowing.

Am I doing the right things so far? I don't really want to spend much more
(or any!) money at the moment so would appreciate advice on things that wont
cost me. Although I'd also be interested to get advice for more expensive
options too though as hopefully I won't always be this broke!

Jasp