Before you go cutting and slicing your tank was built by concept was it not. Some how I dont think the teeth are too small it has to be something else.

You may have to invest in a dremel tool if you don't already own one. Or maybe borrow one. They have a lot of attachments that you can use to cut those slits bigger. I don't know how far apart those slits are but you could maybe use a drill bit to drill holes in between the slits (at the bottom) in an effort to turn two slits into one?

1.5" drain line. The thingamajig is just a check valve with a union on either end for servicing or replacing the check valve. I thought perhaps there was some back pressure but even with just a bulkhead wide open the tank fills before there is barely anything in the overflow box, for example the tank fills to the point of almost touching the eurobracing before there is anything significant in the overflow box. I just tried again and i quickly started dialing in the gate valve thinking maybe I just had to start a full syphon and nope it stay at about the point of overflowing the display.

The drain line as complex as it may look is not actually that many twists and turns and the ones it does have are made of 2-45*'s and everything has a down sloping angle. I dunno perhaps it is the line causing back pressure.

Ya it could possibly be something else still so definitely try to exhaust all possibilities as cutting those grills will be a beeotch.

I know that on my weir which has egg crate in it, after the first year of operations of my tank I started to notice the water level of my tank hitting my euro brace. Upon investigation I discovered that just three holes on my egg crate had plugged up with encrusting coraline and bubble algae and that was enough to restrict flow into my overflow box considerably. Since my weir is so shallow with respect to the top of my tank I really need to make sure the grates on my weir are completely free of obstruction all the time otherwise the water line will hit my eurobrace and possibly even flood the tank.

Yes it was built by concept, I am up for any suggestions!

Yes I do own a dremel great tools! The gap between the teeth is 1/16" which seems really small but what do I know right lol

Is your check valve upside down? Pm sent

Ya, if there was a problem with the drain line plumbing I would have expected the overflow box to flood. From your description it sounds like water definitely isn't even getting into the overflow box fast enough.

Kien may be right about the slats too narrow I hope you don't mind I'm posting the pics you took for others to see I just find this odd for a concept tank I have never heard of this issue before but it can happen

http://i998.photobucket.com/albums/a...8AC87B97B8.jpg

http://i998.photobucket.com/albums/a...8ACDFCD543.jpg

http://i998.photobucket.com/albums/a...8AD755B57A.jpg

Those slits sound really narrow to me.

Hey thanks for posting those pics for me! Yea they are only 1/16" as you can see before those pics I drained roughly 15 Gallons out of the display in anticipation of having to somehow widen those slits. When you look at the one photo you can see a scum line from my dry rock of where the water was before I took out the 15 gallons. From that point it raises to almost touching the euro brace and im sure if left it would go over it had it had enough water. At the point of just about touching the euro brace it really starts flowing into the overflow box but by this time it never equalizes and just runs the return pump chamber dry while the display slowly floods.