I found a product that contains BT called Knock-out Gnats and used if very successfully. It's a soil drench and you use it once a week for three weeks or until your population is under control since it kills the larvae, not the adults, so want to go through more than one life cycle. Some of us are reluctant to use heavy duty chemicals and this solved the problem for me and I haven't had to use it again. I don't know whether it is available in Hungary. Mary Sue