In article , Tim Nicholson
wrote:

Hi, I'm not really even a lurker here - just dropped in tracking someone
else's x-posts but while I'm in the area...

I have a largish pond in the new garden, about 11' radius and approx
2' deep, apart from a ledge about 1' deep and wide round the
circumference. By my calculations this gives me an approximate volume
of 4,300 gals or 19,600 ltrs.

Like the rest of the garden, this pond has obviously been neglected
for at least 5 yrs before we got here, and although there are a number
of goldfish (around 35 we think) and a small number of larger fish
(possibly koi - I'm no expert), they're difficult to see because the
water is a particularlt turgid green colour. I suspect there's a fair
amount of debris on the bottom of the pond which won't be helping.
There's enough plant life round the edges to keep the toads and frogs
happy, and a few waterlilies which bloom quiute spectacularly in the
summer.

Sounds like a fairly healthy water but suffering from the usual small-pond
problem of insufficient large predators. Remove about threequarters of your
fish and you'll probably see a pretty rapid response.

Sunlight supports algal growth, various invertebrates eat the algae, the
fish eat the invertebrates. Cut the fish numbers and you leave enough
inverts to keep the algae down. A few straw bundles, tangled weed refuges
and maybe an inoculation of daphnia will all help.

The fish will rapidly grow/breed to utilise the resource btw, you'll have to
take more out from time to time.

Hth, Cheerio,

--