"john d hamilton" wrote ...
I have got about thirty goldfish in a plastic cold water storage tank
about 4 metres long 1metre deep and about one metre high. It's full of
sludgy mud at the bottom. normally they don't disturb the mud and the
water stays clear. lately though they have been rushing and thrashing about
and the tank water now just looks black. I'm wondering what is the easiest
way to clear out the mud at the bottom of the tank. any suggestions to a
novice most welcome.


but i wondering if all the sludge got really stirred up, and this would
certainly do it; whether the fish would suffer discomfort, and whether
their gills and breathing can filter out all the mud particles, without
any trouble?

I have had the water in a pond, really, REALLY!
muddy, sludgy, dirty, and gunky, and when the s*
finally settles, all the fish were ok.
((You know, like the time when during the
night a racoon while fishing, decided to disconnect
the hose from the pump sitting on the bottom
gunk, , and I, in morning, turned on pumps,
and hour later noticed that that pond pump,
instead of pumping into hose, was just jetting
the water out into the accumulated gunk.**))

my first instinct would be to take a small bucket and keep spooning out
the sludge.

That is very close to what I would do.
OK,ok, I'm a packrat, so I have a fair
number/variety of 'buckets' around
(from 5 gallon paint buckets, to 2 gal.
cleaning, to plastic 'laundry soap' pails,
to 1 gal. thin plastic milk jugs
((very easy to cut off about 1/2 of the
top portion - easy scoop with handle)) ).
I'd kinda gently fill several with the mud,
then leave sitting overnight to settle.
(advantage with this is, if a fish were unlucky
enough to get scooped up, he swiming
on top still safe and can be put back
into his school!)
Then next day pour the top clearer water
back into pond, and dump the mud into
the compost pile.
Gently fill buckets with mud again - repeat.
Repeat as needed until most of bottom
"sludgy mud" is gone.

(meanwhile, the ** footnote.
You know how in tourist sovenier shops
the world around, you can buy these
"snow globes" that have a tiny model
of the city's most famous buildings,
in the globe of water, you shake it up,
and the city is covered in a thick snowstorm?
It finally settles leaving a still & snow covered
scene. Fairly popular items.
((Really, think about it! How gullible, silly, and
mislead we are. How stuck in our ways.
How often is Monaco covered in a snow storm??!
But, if silly tourists buy them, and we do!?,
shops will certainly stock them, and manufactures
will make them.))
Do you think there would be any market for
a globe with a little model of our ponds,
and pond life, and instead of the white 'snow',
black 'mud gunk'. Shake it up and all dirty & murky.
Let settle and our pet fish are visable again?
You think there is no market there?
OK, I'll accept that.)