Hello, I'm new here but figured I'd get straight to the point. I plan on adding an introduction eventually.

I had four frogs. Two Green Frogs, two Bull Frogs. They aren't technically "mine"; they're wild frogs that moved into my garden pond last summer. They stuck around all summer and through hibernation and now that my pond is thawed I was looking around for them. Sadly, I've found already found two of them dead and scooped them, and at this point I have to expect the other two to also be dead.

I want to prevent future frogs from ending up with the same fate. My pond is 3' deep. At the bottom there is a pile of hornwort and a couple of pots with plants in them. There is a little muck, but only what built up over the summer, not more than a half inch. Ice never got close to the bottom, and I kept a small hole open in the ice with a pond heater for gases to exit and oxygen to enter.

I can't figure out why they didn't survive, so I came here in hopes that you guys could help me figure out how to improve the chances of future frogs. One of the reasons I built my 400g pond is to attract wildlife like frogs, toads, birds, and insects, so the last thing I want to see is them dead because they called my pond their home.

Here's my pond last Fall.