I've been lurking in this group for a while and I'm very
pleasantly surprised that it is not full of bots and trolls.

Anyway, I have a pond that has been green since August. It's about 1000
gallons and has 3 small fish: 2 6-inch koi and one tiny 2" shubunkin. I
noticed that all my plants started to look ragged and rot within the first
month of setting up the pond, so I figured the goldfish were eating them
and I set up a 30 gallon plastic tub and put what was left of my hyacinths
and hornwort in it. I stuck a big hose on the pump and connected it to
the tub. Then I added a pipe from the tub back to the pond so the water
could drain back. The plants still just fall apart and die!

Even the water hyacinth has just barely hung on to life; after 2 months I
still only have one. The hornwort just turns dark, sinks and dies.

The pond liner has a peculiar smell: sort of minty. I noticed that it has
imparted this odd smell to the water. Even 6 months after starting the
pond, I can still smell this strange smell if I touch the water. The pond
liner was bought from pricebully.com and says that it is made for fish
ponds. It's 40mil and 10x10.

So to test whether there is something wrong with the liner, I set up a 60
gallon plastic pond about 20 feet from my big pond. The second pond
doesn't smell funny, but I get the same results. One water hyacinth just
kind of stays alive and doesn't spread. Hornwort just sinks and rots.
There are just a couple of platies swimming around in there to prevent
mosquitos from breeding in the pond. This was in september.

Now by october, I was figuring that cooler weather would slow down the
algae and maybe help the plants some. Also, with the rains stopping, there
would be no more run-off getting into the pond. Now it's november and the
temperature rarely tops 79. Overnight lows are 50s and 60s. Still both
ponds are green and I only see fish when I feed them.

The tap water around here has kind of high phosphate and nitrate: both are
typically over 10 mg/L. I use this water in my fish tanks and the plants
do well enough, even the hornwort, which is not a difficult plant anyway.

Against the recommendations of LFS salespeople, who are pushing RO/DI
systems, I use regular tap water in my lightly stocked 55 gal marine tank.
The fish seem fine, there is lots of coralline algae and several species
of macroalgae are thriving in my refugium. I do not keep corals and other
expensive invertebrates because I'm afraid they're being unsustainably
collected.

Anyway, I just can't figure out why my pond is always green. I'd like to
see the fish more than once a day when I feed them!