[DJ88]

First question. How far below the waters surface is your spraybar "overflow"?

For example if it is six inches below the surface you will need to be able to hold approx 20 gallons in your sump as this much water will flow back into your sump if the power goes out due to siphoning from your main tank. This means you will only be able to have 10 gallons of water in your sump.

48" * 18" * 6" = 5184/231 = 22.44 gallons draining to your sump in event of a powerfailure.

33g - 22.44g = 10.56g gallons max allowable in your sump so you don't overflow when the 22.44 gallons returns to the sump.

10.56g * 231 = 2439.39/36" = 67.76/12" = 5.65" max allowable water depth in sump. So your baffles can't be any higher than 5". If they are higher your sump will overflow when the power goes out. If you put the lower baffles at 5" high then make the area of the sump where the retun pump feeds from 12" long, you will have 12" * 12" * 5" = 720 720/231 = 3 gallons of water for your pump to work from. If you concider that the pump will be about 2 inches above the bottom of the glass you will only have an actual 12" * 12" * 4" = 576/231 = 2.49 gallons of water for the pump.

That is not a lot of water.

The only way you will be able to use the 33 as a sump with your tank is if you have the tank drain in and get rid of the second set of baffles and make the right hand 2/3rd's of the tank as the drain area. You will not be able to have a fuge in your 33. The flow will be too fast and too shallow.

IMO

If you were to have the depth of your sump at 12 inches, in the minutes after the power goes out you will have 11.88 gallons of water overflow into your stand.

12" * 12" * 36" = 5184/231= 22.4 gallons of water in the sump. With the previous calculations I made an the spray bar is 6" below the waters surface you had 22.44gallons drain into the sump. this makes, 22.44g + 22.44G= 44.88Gallons into your sump. The sump only holds 33 so..

44.88g - 33g = 11.88 gallons overflowing Everytime you lose power.

All these calculations are not taking into account the volume taken up by gear/glass in the sump. Keep that in mind. More space taken up means more water going outside the sump.

Either you are going to want a much larger sump or else have your spray bar an inch or two below the surface of the water(if not closer). This is why overflow boxes are used. They limit the amount of water draining into your sump by having bottom of the teeth 1/4 - 1/2 inch below the surface of the water. By drilling anti-siphon holes in your return lines at this same depth you will have a very minimal amount of water draining into your sump.

Hope that helps.