Estimate how much display water may return to the sump during a power stop.
Open live calculator →A 120 × 50 cm display dropping 2 cm sends about 12 litres toward the sump.
Add plumbing volume and confirm with a supervised power-off test.
Calculate the water contained in a chosen drop from the display tank's water surface as a starting sump-capacity check.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
Test the real system under supervision.
Include water held in plumbing.
Keep return outlets and siphon breaks maintained.
When return pumps stop, water above the overflow level and inside plumbing keeps siphoning into the sump. If the sump lacks spare capacity for that volume, it overflows onto the floor.
Drill or position a siphon-break hole in the return line just below the water surface, keep return outlets high, and set the overflow weir so only a small surface layer can drain.
With the sump at normal level, switch off the return pump and watch where the water settles—supervised, with towels ready. Repeat after any plumbing change; the calculator is a planning estimate, the test is the truth.