I have had catfish before, about 50 and for about 5 years then a winter freeze took them.
The only chemical that I use to control the algae is copper sulfate about 2 time a year and I have already treated the pond once this year.
Also I have a fountain for the summer and it converts to a deicer for the winter, it has a long tube to pull the water from the bottom for both summer and winter. This has work great for 7 years now.