Fungus gnats and swamp tank

Can fungus gnats live in stagnant water? I have a mini >1 gallon size cube I have some dirt, aqua soil, bladder snails, and pothos/peace Lilly’s growing out of with a handful of salvinia. I just kinda let it do its thing, and top it off with tap water and watch the bacteria bloom and clear up over and over. It doesn’t stink.

It’s next to my window box that I stick my leftover green onions into and have some lettuce growing in.

I’ve been treating all of my house plants with mosquito dunks. I have a five gallon bucket with a whole dunk in it, I just top it off with conditioned tap water and use that to water my plants.

Should I top off the swamp tank with mosquito dunk water?? Can the fungus gnats even live in or on the swamp tank?? Would the mosquito dunk bacteria crash my cube?