Selecting the Correct Overflow

OK guys and gals, Scott V. here with you. I am going to attempt to make a document to walk you through selecting on of the Glass-Holes overflow kits! Do please feel free to email me at info@glass-holes.com if you think of anything that can make these guidelines better! We are all about making sure that every tank gets the correct overflow!

#1 The first thing you will need to decide is what you want to keep in your tank! This really dictates the amount of total flow you will need in the display. The accepted minimum is 10 times your tank volume. This works for softies and LPS, up to perhaps as much as 15-20 times. For high flow critters such as SPS, 20 times plus is accepted as normal nowadays (because it works!).

#2 So multiply your tank volume times the amount of turnover you will need. Lets say we are setting up a 75 gallon SPS/LPS tank, we will need about 20 times our tank volume in flow, the upper end for LPS and lower end for SPS. 75 X 20 = 1500 gph total flow in our tank.

#3 Decide how to implement that flow. I do want to differentiate now between flow in the tank and flow through your overflow and sump, they are not necessarily the same! You can run all your flow through the sump, but you can also flow less through your sump and add supplemental flow (powerheads or closed loop) to reach your total flow in the display. Advantages to running it all through your sump: simplicity of setup, only have to worry about one pump, no powerheads in the tank, no extra drilling. Advantages to closed loops or powerheads: less energy use (you are not pumping the water up against gravity), more adjustability in the system, and less microbubble issues in the return. Example on the last point: If you have the 75 mentioned above with a 10 gallon sump, running 1500 gph through the sump will present quite the challenge to keep bubbles out of the return pump. The slower the flow relative to sump volume, the longer the bubbles will have to dissipate out of the water before reaching the return. Of course there are ways to handle this: baffles, foam, filter socks etc. All that longwinded stuff said, a minimum of 3-5 times your display volume per hour through your sump is more than sufficient for filtration purposes.

#4 So now you have an idea of how much flow you need for your tank and how much of that flow you want to run through your sump, so how to pick an overflow? One method is just match the flows up; for 600 gph we could use the 700 kit. But do keep in mind stuff happens. Lets say a large snail manages to crawl into the box and plug the drain, it would be nice to have a backup! So, if you are from the school that believes in 100% overflow redundancy, do consider going the next size up, the 1500 kit in this example.

#5 Choosing long or short bulkheads. The long bulkheads are used in tanks with glass thicker than 1/2" and will need to be cut. The short bulkheads are fine as they are for 95% of applications where the glass is 1/2" or thinner.

Some links on aquarium flow:

WWM Flow

WWM Overflow Redundancy