First lil' pond, need some pointers

Made my first mini ponds with some bourbon barrel planters the other day and I'm struggling! The ponds are producing a pungent pungent sulfur stank, the mosquito larva are partying, and my small fish population is dwindling. Before I drain these things and call it a day, any pointers on keeping them healthy and not becoming a rotten egg smell generator?

More info on my setup and things I've tried so far:

- Each pond has a water lily and a pickerelweed plant that I got from a neighbor's healthy pond. I removed them and cleared out any dead/decaying parts a few days ago.

- Plants are in aquatic plant pots with like 2/3 topsoil from the backyard and then 1/3 pea gravel

- Running a 300gph pump in each pond on a low flow rate setting, using a water-bell nozzle attachment

- One pond has 2 small goldfish, the other no longer has fish but did have a few minnows

- Poured in maybe a capful of barley pond clarifier a few days ago

- Just dropped in a mosquito dunk in each

Any help is super appreciated!