A sump is actually really basic and simple though it can be a little overwhelming searching online. First thing to know is bigger is better, you have a 15 gallon tank so a 5-10 gallon would make a decent sump 10gallon being a better option. The second thing you need to know is you need to make sure your sump will fit where you want it this goes hand in hand with lesson one. Once you have the size sorted out you need to have an idea on skimmer size. Do some searching online for skimmers to fit your tank and build the sump with the dimensions they list in mind, make the skimmer section a little larger to make life easier. Now with that sorted you need 4 pieces of glass cut to fit front to back inside your sump tank. The height will be dependent again on your skimmer, the recommended water depth will tell you how high to make your dividers but keep in mind your not gonna want them all the way to the top as you want to be able to store excess water that will drain from the display tank in the event of a power failure. My baffles/dividers are approximately 2/3 the height of my sump tank. Now you just silicone the dividers in place, the first section where the skimmer goes and where your tank will drain into on needs on divider. Then the divider between the last 2 sections (if you want a refugium that is) is made of 3 panes. The 2 outside ones go right to the bottom and the one in the middle is raised an inch or so, this is known as a bubble trap. Hope this helps some, feel
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