After setting up dozens of tanks, the gear that earns a spot is the stuff you stop thinking about. The overflow box is one of those purchases where the right size matters more than the brand name.
What it does
It moves water from the display tank down to a sump without drilling the glass.
How to choose
Size to the tank, not the shelf. For a typical 47-gallon setup you want an overflow matched to your turnover; a unit rated for 499 L/h of flow (around 25 W) covers most stocking levels without over-driving the water. Check a solid gravel vacuum water changer for a small tank for the bigger picture before you commit.
Setup tips
- Position it for even flow or heat distribution — dead spots are where problems start.
- Prime or rinse media in tank water, never tap water, to protect beneficial bacteria.
- Build a spare into the budget; when it fails at 2 a.m. you will want the backup.
Maintenance
Clean on a schedule tied to your water change — every 5 weeks is typical. Rinse reusable media in old tank water and replace only what is truly spent. Pair it with the molly care: livebearers that love hard water so the whole system stays balanced.
Scaling up
In a tank over 55 gallons, match the overflow box to the full water volume and stocking load; undersizing here strains the whole system. Build redundancy so a single failure does not take the tank down.
