Conclusion

Turn-over time is defined as the time it takes for an aquarium device to process 99.9 % of all tank water. If that device has a flow rate of $F_0$ gallons per hour, and the tank has a volume $V_0$ gallons, then turn-over time $T$ is

$$T = 6.90776 \cdot \frac{V_0}{F_0} \mbox{~(hours)}.$$