The tank does have a filter chamber,i designed it so its easy to change to water, so i can do that to help. Thanks for the name, i googled them and yes it is the culprit!!! At night after i turn the lights off i will see one or two of them flying around , but shortly after my duo wake, and i see no flies in the morning. I am headed to the sporting good store to buy some" no see um" fabric for the top, im all for free snacks, but not im my part of the house.