UK is in the Western hemisphere, it is currently mid-winter approaching
Spring. We are about 40 miles North of London. To date this winter, no snow,
ambient temperature varying between 32 and 50 degrees F.
I have a small pond, self-dug, about 800 gallons, made about about 10 years
ago. It did have an eclectic mix of fish, but two major catastrophes
occurred, both within the last year.

1/ My birthday and Father's Day were a week apart last year - my family
bought me several small Koi from THe Japanese Koi Co - UK fishery about 2
miles away, the largest Koi supplier in the UK. Within a week my pond fish
mostly died - I was left with just 5 fish, and had major problems
hospitalising them, completely draining the pond, totally cleaning and
re-conditioning.

(Have since discovered that the Japanese Joi Co (Henlow, Bedfordshire) is
locally known as the One Stop Shop - customers only shop there once .... my
experience is not uncommon).

2/ Having found two more reliable suppliers (one, 25 miles, the other, about
10 miles away) restocked the pond last year with a few small Koi. They
thrived and survived just fine, till last week. Then came the heron ....
I'm now down to just 3 fish left. My carelessness - forgot to re-cover the
pond with a net frame I made.

With 10 years or more pond-keeping (and, prior to that, near 30 of
tropicals) I am fairly competant - pond fish in particular, 9 years with no
major casualties. I have water testing kit, but have yet to successfully
defeat blanket weed. Despite the low temperature, blanket weed is thriving,
I'm taking it out by the net-load. My water is clear and pure, and within
limits for all tests.

I've had the "electronic" water treatment (the coil thing round the water
outlet from the filter) for several years - cost me £99 (about $170) and
it's worthless. Enzyme treatments do work, but at $30 a throw, expensive for
just a few weeks freedom - and I'm not happy about the reduced oxygen level
when they're employed.

Am thinking about the "I Tronic" solution - in UK, £120, ($218) but - read
the reviews. This works chemically by passing pond water over a copper
anode (thus introducing a copper salt into the pond). Seems like it's a
VERY fine line between annihilating the blanketweed (which it does, VERY
effectively) and poisoning the fish ... just a very few parts per million
and the water becomes toxic to fish.

I realise I haven't posed a question - it's a mix of subjects and I hope
some contributors will add their comments and experiences to share the
combined knowledge and wisdom.

Sincerely, Len.