Preventing Midges / Flies Entering Raw Water Tanks

We are looking for an innovative way to stop midges from populating our tanks. There are a large number of indoor uncovered Granular Activated Carbon absorbers (GACs) within concrete tanks (generally 4×7 metres), that attract midges (Chironomid) which lay eggs on the surface of the water. These then populate the GAC as larvae and in turn return back to the surface to pupate and re-emerge as flying midge. Our teams spend a lot of time making sure our water is of the highest quality and we take steps to prevent the midges entering the water network. We understand from previous studies that ideal conditions for the midges are calm water surfaces. The ideal solutions may disturb this environment, be easy to install and would not create a lot of noise or harm the tanks. More details can be found here: http://waterinnovation.net/opportunities/midge-opportunity/#more-323