Gervahlt is your name by any chance reference Gevolt/gewalt?
and Vitaly I've had luck with lowering the water level but it depends if you have powerful fish, I know how you feel with the little holes because i had a snakehead once that dissapeared found him a week later under my bed all dried up, I thought he was hiding in the tank, if I knew he was out I probably couldve saved him which is annoying.
Glass lid would probably be your best bet but make sure you keep it clean algae and Limescale will build up depending on the hardness of the water which will block the effectiveness of the light, which I assume for a planted tank is most important.