Adding 2nd sump. Please help!

[reef dreamer]

I have a 55Gallon long tank which is in transition to a reef tank. I had been using a 10Gallon glass tank as sump, and only reason for this was the limited space in the tank stand. Recently, I have just added another 10Gallon glass as the second sump sitting next to the old one in order to increase the capacity. The old sump is placed 7 inches higher and the water is delivered to the 2nd sump through DIY U-tube. The return pump is in the 2nd sump. I realized this setup has a potential problem as the followings:
1. If the water is depleted the vacuum in the U-tube will break.
2. The water level in the 1st sump is always low just a little above the water level in the 2nd sump therefore not utilizing its whole capacity.
3. when I turn off the pump to feed the fish the water level rises only in the 2nd tank posing potential flooding probem.
Is there any way to setup these sumps so that the water level is equally distributed and the added capacity is fully utilized?
I want to use the increased space as the refugium. Your suggestions will be really appreciated. Thanks!

 

[captained]

A couple of thoughts...
I have a "dual" sump-refugium but I built an acrylic-lined box for the sump that is a little taller than the 20 gal refugium tank. I was trying to maximize space and built the 5-sided box to fit my space, but a trash can would work. I put a bulkhead fitting near the top of the box, so that the return water fills up the sump then spills over into the refugium (you can see my drawing.http://www.wdcnet.net/edward/sump-pop.html) This means the sump side is always full to the top (where the bulkhead fitting is.) This would solve problems one and two for you, and your refugium would have the water level vary up and down from evaporation, etc.
I also put in a check valve on the main return so that I get negligible water coming back down into the tank if I shut of the pumps. This was a challenge since most check valves require more pressure to "open" than you normally have. I used a Raritan valve for boats that you could open up, and cut off part of the spring inside- it works, but you have to have it positioned vertically or the ball inside the valve won't drop and close it.
Have fun!