Here in the UK I have 4000 gallon (18000l) pond stocked with goldfish &
orfe. It is very rarely clear, it almost made it briefly in March, and
as usual has been pretty murky since.

I have a couple of filter boxes shifting 1800g/hr, which are very
effective biologically, ammonia & nitrite never measure anything other
than zero. There's also a 2x9W UVC.
There's a good selection of marginal plants & lilies, and I got some
WH's last week.

In previous years I've tried adding potash (a product called LoSalt, 66%
KCl, 33% NaCl), which helps a bit, but didn't really clear the pond. The
plants all seem to be lacking in the vigour one expects of aquatics.
I finally got some time to look into the details, re-read loads of notes
taken from this news group and the 'net over the years, and decided to
check if I had some other limiting nutrient to plant growth.
PO4 measures ~0.5ppm, Nitrate ~3ppm.
Plant behaviour hinted at iron problems, so I got an iron test kit,
which confirmed absolutely zero free iron, zero chelated iron.
As the pond is generally topped up by rain water, I also suspect other
trace elements may be zero too.
So I bought a box TE, the contents of which a
Boron 0.1%
Copper 0.25%
Iron chelated EDTA 3.3%
Magnesium 7%
Manganese 3%
Molybdenum 0.005%
Zinc 1%

So the question to any experts out there is,
1) Are any of those TE's a problem / toxic to fish at these levels?
2) Recommended dose rate, I've been working to 0.1ppm iron, although the
test kit suggests 0.25-0.5ppm for chelated iron.
Whatever I add is back to zero the next day.

If I want to add iron only, is FeS04 any good? (I suspect it just
precipitates out straight away?)
Or do I need to get some chelated iron and keep dosing until the level
stabalises?


Other parameters are pH=8.0 rock steady, KH=100ppm, GH=120ppm,
salt=0.03% (I've moved away from salt dosing in general, all the fish
are happy & healthy without)


Cheers
--
steve