How to Keep the Water Levels Even in a Fish Tank Sump

The water levels in an aquarium sump rise and fall with evaporation and additions of water. If the aquarium uses overflows, which many do, then the water level in the aquarium will remain the same while the level in the sump will fall. Only fresh water evaporates, so water loss in the sump increases the salinity in the system, which can hurt the animals.

Things You'll Need

  • Jug with an airtight seal on one end
  • Knife
  • RODI or distilled water
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Instructions

  1. Water Tight Jug

    • 1

      Choose a jug for the project. The jug must have an airtight seal on one end and be taller than the optimum water level in the sump. How much taller depends on the room you have in the sump. If it is very tall, tie it down so it doesn't fall over. The jug should be made of food-safe plastic; do not use metal since it will corrode. A cleaned, 2-liter soda bottle works well.

    • 2

      Cut two holes in the jug: One at the optimum water level and another below this hole. Alternatively, you can leave the bottom of the jug open instead of drilling the lower hole. The hole at the water level will let in air when the water drops below it, allowing the water in the jug to flow into the sump.

    • 3

      Fill the jug with fresh water. Reverse osmosis de-ionized (RODI) water, or distilled water, is best. Tap water often has nitrates and phosphates in it that can encourage nuisance algae growth.

    • 4

      Turn the jug upside down and place it in the sump. The airtight seal should be on the top and the holes should be on the bottom. The seal will create a vacuum and the water will stay in the jug until the water level falls beneath the air hole. When this happens, air will get into the jug and water will flow out through the bottom hole. Therefore, the water will not drop below the air hole.