sump overflowing

[o0jmadr0x0o]

I purchased the tank and sump used and it was pre-drilled, guy told me it was great as i was. but he didn't mention the overflow noise because i guess it didn't bother him. anyway i was told to make it a "herbie" overflow and that works great, totally silent. now my problem is that my full siphon drain has to be parallel to the floor or it makes a whirlpool and is way loud. but being parallel to the floor, too much water drains into the sump if my return pump is turned off. i made a new sump with a 20l that would have been able to handle the extra water but it wont fit into the stand because of the center brace. so i cant get a bigger sump in there. the tank is up and running so its too late for an overflow box. do i have any other options beside draining the tank and taking everything out to fit the 20l sump(really want to avoid doing this).

http://i153.photobucket.com/albums/s218/o0jmadr0x0o/20140212_185246.jpg (http://s153.photobucket.com/user/o0jmadr0x0o/media/20140212_185246.jpg.html)

[rfgonzo]

lower the water level in your sump, so that when the power goes off water does not overflow. You should be able to do this by lowering the water level in your return section.