I don’t have a basement though and I really want to look at the fish. I’m considering a 29-gallon tank and not replacing the goldfish that are lost to predation the last month. I figure with the bubbler and filter, I should get through March since all the fish I have are pretty hardy.
Jack, can I point out that your plecos are (a) tropical, so they need a water temp of at least 75 F., and they really shouldn’t be in an outdoor pond unless you live in Florida or California, and (b) really huge and messy, so they’re not gonna be happy spending the winter in a 29?
Neither will your koi, for the same reason, unless they’re still really small, like only 3 inches long.
And–more bad news–your goldfish that you keep having to replace aren’t being eaten, they’re probably simply dying from poor water quality. You’ve got “several” plecos in a pond (how big is it, BTW?)–plecos put out an extraordinary amount of poo.
Do you know about something called “the nitrogen cycle”, which is where you use friendly bacteria to consume the toxins (ammonia and nitrites) that fish produce, both through their poop, and by excreting it through their gills. Your goldfish, in other words, are being poisoned by their own wastes (and by those of their tankmates, especially the plecos). It doesn’t do a bit of good to simply plunk a filter down into a pond without knowing how it works.
http://www.actwin.com/fish/mirror/begin-cycling.html
And simply having plants in the pond isn’t a guarantee, although I’m sure that’s what the guy who sold them to you told you.
How often are you doing water changes, which is where you take out some dirty water and put in some clean water? There are other kinds of wastes that build up, that have to be physically removed, called “dissolved organics”. A filter won’t take them out, and neither will plants.
Have you got this pond set into the ground, or is it a plastic pond up on a deck? Have you ever actually seen a garter snake eating one of your goldfish? I don’t think we can blame this on the snakes.
Goldfish also die of shock from being simply dumped into water that is (a) a different pH from what they had at the pet store, and (b) a different temperature.