Hello, aquarium enthusiasts!

I live in Washington DC and have a 25 million liter short rimless fish tank which I'd like to stock with plants and animals. Annoyingly, it's only about 45cm deep at the shallow ends, so I'm not sure what would work best.

It's also outdoors, and obviously a bit too large to move. Please help! The algae is going NUTS, so I'd like to prevent that. Plecos? Saltwater? Idk, this kind of isn't my field of expertise and my cabinet is really busy with this whole "Texas secessionist movement" bullshit.