How Much Water Do I Put in My Aquarium Sump?

The exact amount of water you need to add to your sump will vary based on your design. Sumps filters are aggressively DIY creations that may focus on several different roles depending on how you want to use your sump. However, once you design and assemble your sump, you can figure out easily how much water you will use through a careful trial-and-error process.

  1. Design

    • Sump filters can fulfill a variety of purposes. When designing your sump, consider how much room you have, what you want to use the sump for and what equipment you want to use in your sump. For example, most aquarium hobbyists hide their sumps within the fish tank stand, restricting their size. Additionally, sumps can hide unsightly aquarium gear. You will need to know how much room you require in your sump for such things, like protein skimmers, reactors and heaters. Measure the sump and plan it carefully before assembling it.

    Assembly

    • You must assemble your sump fully to figure out just how much water it will take to fill it. Glue all of your baffles in place and set up all of your equipment. Complete the plumbing, since you will need this in place to determine how much water to use. Attach all hoses, and fill or prime all pumps or filters. Do not turn anything on until you have a permanent marker ready.

    Marking

    • Before you turn anything on, mark the water level on the outside of the sump with permanent marker and label the line "pump OFF." Make sure every filter is full of water and every pump is primed. Then, turn on all of the equipment in the sump. Once you're sure everything is running, turn on the return pump. The water level should start dropping quickly. Once the aquarium fills up enough that water starts coming back through the drain, let it run for several minutes. Then, mark the water level and label it "pump ON."

    Running the Sump

    • When you operate a sump, some water will evaporate away. Since saltwater aquarium hobbyists usually are the ones with sump filters, this will make your saltwater saltier, because water evaporates, but salt does not. To counteract this, top off the sump with purified water, like RO water or distilled water. Always double-check the salinity after this with a hydrometer. Never fill the sump beyond the lower, pump ON line. If you fill beyond this line and the power goes off, your sump will overflow and you will find yourself with a flood and/or an electrical fire.