On 31/08/2020 17:28, Chris Hogg wrote:
Blanket weed, Spirogyra as TNP says, is an alga, and as such is a
simple plant. Plants thrive on nitrogen, nitrate to be more specific -
it's one of the three components of most garden fertilisers. If you
have a lot of nitrogen in your pond water, blanket weed will flourish.
There are several potential sources of nitrogen in a pond: run-off
from nearby flowerbeds that have recently been fertilised; rich garden
soil that has been used for potting up pond plants; lastly, and
probably the commonest - fish crap. That last comes from being
over-generous with fish food. When I had a pond in my previous
property, I never fed the goldfish. They never got very large, but
survived and bred quite happily, the water didn't go pea-green in
spring and I had very little blanket weed.

There's another source of nutrients: Tap water. If you have to top up
your pond in hot weather as the water evaporates all the nutrients get
left behind. There isn't _much_ nitrogen in tap water, but there is some.

(I must rig up that rain water diverter...)

Andy