try mosquito dunks, i love them, all natural way to get rid of mosquitoes, flies and gnats. they're supposed to float in your pond and slowly disolve, but i crumble one up, and thats enough to cover 8 to 10 plants, just sprinkle the little crumbs evenly over your media, and they slowly disolve as you water the plants. the big gnats eat it, and so do the maggots, it makes them unable to reproduce, or pupate, and its totally harmless to birds, fish, and people