Mosquito fish disappearing? and Algae

I have two barrel a higher one pouring to another. The higher barrel
have mosquito fish. And the bottom one has goldfishes. The mosquito
fish has been disappearing, I can't seem to find them.
The upper barrel also has alot of algae.

I am having some kind of tiny bugs that jumps on the surface of water.
Also I see something like looked like adult mosquito but a white/green
color. What are these?

Would it help if I put a goldfish in the upper barrel to clean the
algae and various bugs? The bottom barrel with goldfish is noticably
cleaner.

Thanks!