"Geoff" wrote
We have a small (2.4 m dia. by 0.5 m deep) pond in our back garden and it
is
full of weed and lillies so there's one or two fish the heron missed.
Although the pond
was first made some years ago and had been earth filled, 4 years years ago
I
dug out all the earth and lined the concrete (cracked) with a pond liner.
Tufa to below the water level and over the concrete sides holds the pond
liner in place.

We are hoping to clean up the pond so I am seeking advice and
recommendations for a vacuum cleaner/filter to clear the muck from the
bottom.

I use a swimming pool pump and strainer as a vacuum for my pond but with
yours being a fare bit smaller it would throw all the water onto your lawn
before you got back after turning on the power. :-)
The smaller hand pumps etc, don't work well so it's probably better and
easier in the long run to catch the fish, empty the pond ,especially if you
have a pond pump to do the work, and then get in and scoop out all the muck
with a plastic bucket and dustpan. Filthy two person job but you expect
that. Then refill and replant your plants keeping only the best bits.
A filter will keep your water "sweet" and clear but you will still get
solids building up on the bottom, leaves, waste, and general detritus. Any
good watergarden shop will advise the correct size for your pond, and
remember, it works through the action of bacteria so it shouldn't be turned
off for more than a short while once started. If it does get turned off for
a long time (e.g. pump breaks) then you have to thoroughly clean it out
before restarting as the bacteria will have died. Probably need a good
cleanout every early spring anyway.
Give your fish somewhere to hide, a cave or upturned clay flowerpot with a
chunk out the side or something.

--
Regards
Bob
In Runnymede, 17 miles West of London