u mike

I made cardboard baffles to get the size right before cutting the acrylic for mine.

The size and spacing of the dividers has a lot to do with the equipment you are planning on keeping in the sump. You need to know the dimensions of your skimmer and any pumps or reactors that you plan to keep in it. After you know that, then you can space the dividers accordingly. On the melev's reef website, he has a bunch of sump ideas that you can use as a basis for designing yours.

Phil that works. The key to the baffles is making water go over a baffle then under to regulate water height and keep bubbles from getting to the return section. the first baffle should be set at your skimmers optimal height unless you are going to set it on a pedestal, but don't put first baffle lower than needed skimmer height. and you want the return section as big as you can as this is where the water level will fluctuate with water evaporation. are you planning on doing a fuge? it should have a baffle pretty much to the top of the tank since water in this section will be going very slow compare to the skimmer section. flow through sump and width of sump is what will determine baffle spacing.

When you have several baffles in a row like I illustrate on melevsreef, you need to make sure they are 1" apart and no less. That is very important as it stops microbubbles from slingshotting into the next section.

That glass tank link I gave you two days ago has an eggcrate section so the refugium and return share the same water volume. This is especially useful on smaller sumps like a 20g long.

Please be sure you read that page very carefully, including the guidelines of how wide to cut the baffles so that they do not crack the tank.