Getting a stable Fuge

Based on your photos your overflow does not appear to be of the "continuous siphon" variety, but instead the "siphon break" variety.

If this is the case you will 99.999% never get the overflow and return rates to match.

What you need is an HOB continuous siphon overflow such as those made by Eshopps and CPR.

 

Another solution would be to drill the back wall of your tank and run the drain directly from that. If you look in my gallery, I have pics of my overflow drain. I box is "needed" but does provide for some surface skimming. Without the box, it's no different than the drains you see at pet stores; it also becomes a continuous drain and doesn't have the chance of siphon breaks.

 

I think your biggest restrictive point is the overflow box and siphon itself. One my previous reply, I would suggest using a drilled back tank and going with a continuous drain and going away from a siphon based overflow. Don't get me wrong, I have a siphon overflow on my 150G tank, it's a CPR CS-100, but it has an aqua lifter to make it a continuous siphon that gives me close to 700GPH turnover.
To give you an idea, my 20G has a Mag7 return in the 10G fuge. I have 1" PVC drain that splits 2 ways into the fuge, and 3/4" return that is connected to a chiller. I get about 400-500GPH after the head and restrictions.

 

How do I go about making a continuous siphon overflow box/siphon? Or would this be something I would just have to purchase? With my tank only being 30 gallons I don't think I would need much more than 200-300 gallons per hour for the flow.

 

I kinda want to stay away from drilling my tank at the moment. Though it does sound much simpler. Is there a DIY for a continuous siphon with an overflow box? Or can one be purchased for like $50-$100?

 

Reef Aquarium Filtration: Eshopps Overflow Boxes

 

Why do you have a T. shouldent the overflow come straight down into the fuge or sump and then one return line straight back to the DT. Wouldent this equalize the flow.

 

You could make your's a continuous siphon by drilling a a small hole into your siphon PVC at the top and glueing an air nipple into that hole and attaching an aqua lifter pump to that. That will give you a continuous siphon.