Hi
I kept tropical fish untill the "polar vortex " of 09 wiped out the entire stock so went to GF They had some "feeder" types at 7 for a buck . Got the 7. Spring of 11 needed some repairs so pulled the fish out Totaled 104!!
Haven't any long term experience with GF but they obviously multiply?? They also grew incredibly fast several topping a foot!! Interestingly had another disaster this spring (timer failed on tap water) so down to zero again I added 10 feeders and some Rosy red minnows and already down to 5/9 think I'm feeding a heron . had a terrific problem with that when I first started the pool
Good luck with balancing them out !! gary

I'm far from a Guru but I have a 2,000+ gal Koi pond. My wife loves Goldfish so we added a dozen about 10 years ago. Every year we have to give away at least 100, sometimes 200, to a friend with a 4 acre pond. I'm sure it is a treat for his game fish but we can't have that many and expect them, or the Koi, to get very large. It is a challenge to catch them a couple times a year. I guess we keep 15 to 20 of the largest (about 7"). Depends on how big you want them to grow. We never had a problem until early this Spring, when a Great Blue Heron visited the pond on a weekend we were away (was there when we returned). It took 5 of the 6 Koi ranging from 12 to 18 inches as well as all but 4 Goldfish. Those 4 Goldfish quickly reproduced at least 50 to 75 little ones. I'm going to have to buy more Koi. I used a net that I have for our grapes on the water a couple months. Haven't seen the heron but I suspect it will likely show up again.

There can't really be a general rule. It depends on your goals. If you want them primarily as pets then 4 sounds good. In 1000 gals you won't even need a filter.

If you wanted lots of color, lots of energy you could keep 100's with decent filters.

If you wanted to grow big fish then you could have 10-15 and cull some that didn't grow very well. You would need very good filters and feed a lot of food.

Be careful about filters. Any filter that says it's for a certain size pond is probably not a very good filter. They're trying to sell to people who don't know much about ponds. Instead check out Trickle Towers, Moving Bed, and Bakki Shower filters. These have tested to be about 30 times better at ammonia conversion than the filters with submerged pads.

Thanks for the responses sorry i didnt respond sooner but i never received notification of responses despite having ticked the box for it.

I have a similar size pond to yours, 1100 gallons. No matter how few goldfish you start with, in a couple of years you will have something like 15 medium to fully grown fish and a whole bunch of smaller ones. I found that after a few years the number of babies that survived dropped. I have a home made biofilter with a 600 gallon/hour submersible pump in a prefilter. I lost all of the fish when my thermopond heater failed and I started again with 8 high quality Sarasa comets. They have not yet bred. I also have rosy reds.

Well, 50 gals per goldfish is said to be a good rule of thumb which would give you 20 fish. I wouldnt go much over 15 though. I have 10 in 800 gals and that's about right. Enough fish to school together nicely, but not too many. Esthetically, too many fish crammed together looks bad to me (hundreds?? seriously??) They get stressed and dart around instead of schooling together, and dont give you a relaxing feeling to watch them.

You want enough fish that they will practice natural birth control (ie they'll eat up all the eggs after spawning) but not so many that you have to worry about water quality and high mortality from bad water conditions.

Esthetically, too many fish crammed together looks bad to me (hundreds?? seriously??)
Different folks, different strokes. Some people think having a pond at all is crazy so I don't like to throw stones.

50 gals per fish is a good rule of thumb. So is 20, 70, 100, 200 and all the numbers in between I've seen people post. All great rules of thumb.