we have one, and it's exactly as you say: toilet tank innards. i'll ask my husband what the details are, but our pond is much smaller than yours, probably around 200 gallons. before then, we had a drip line that came on with the watering system kicked in.

-ming

My DH mounted a stock tank filler bought at Tractor Supply to work on the pond.

Since we live in Florida and have dry times of the year,we used it for when we went away for over a month. Seemed to work nicely as the we were told we did not get rain while we were gone and the pond was still full

Check the link below for auto fillers.
"Horton"

Here is a link that might be useful: Auto Fillers

What does DH stand for? LMAO....I think I know but...My head is always in the gutter...so just acknowledge me and I'll keep laughing to myself LOL.....Dave

I hope this doesn't constitute advertising (which is not allowed), but I have successfully used the Laguna float valve in my pond. It has done an excellent job of maintaining the water level exactly where I want it and is not expensive. I cut into a water line that feeds well water to a hose bib near the pond attaching it with a small diameter flexible pvc line and a "T" connector. This eliminates the need for me to treat the water. The tricky part is positioning it so it maintains the water at the level desired. I sandwich it between the liner and a rock at the edge of my pond in an inconspicuous place. It is widely available so you should have no trouble finding one locally or online. Just Google "Laguna float valve". One word of caution, the little rubber disc that serves as the seal comes off easily, so you may want to glue it in place.

Dave, it stands for darling (or dear) husband...when things are going well at the homestead. Otherwise, continue using your wonderful imagination. :D

Brenda

so i think it depends on how much is evaporating from your pond every day. if you have a low to moderate surface area to volume ratio, i think you'd be fine in maintaining what's lost...not for filling your pond, though. we use a garden hose with an adapter to a quarter inch tube and it hardly turns on.

-ming

If you still need one