Tiny little winged creatures (gnats?) are killing my zinnia and basil plants!

Winnipeg is not letting go of winter, so all my seedlings and growing fast and are all still inside.

A couple weeks ago, I noticed that in my greenhouse (an aquarium with fluorescent lighting) tiny little bugs that look like fruit flies started showing up. Shortly after, the leaves on both the zinnias and basil plants started to get spotty, lose their bright green colour, then dry up leaf by leaf. Most are hanging on, but they are looking mighty sad. temperature, light and water levels are dead on, so I’m assuming the bugs are killing the plants.

Any ideas on what these little guys are and how to get rid of them? They look like fruit flies, but are half as big and aren’t into fruit.