Fill tank to the top

[Pysiek]

My tank have been running for about a month right now. Close to the top I have a small gap where you can see the top of the water. How do I fill up to raise water level in main tank so it will go all the way behind the black rim on top? Do I need to raise overflow box also? I have ATO.
Thanks

[horwitzs]

The overflow box dictates the water level in the main tank. Either raise it, or block the overflow openings at the bottom so the water has to get a bit higher to spill over.
And put lots of towels on the floor around the tank while you do the trial & error to get it right where you want it :)

[laugh]

Or get a bigger return pump.