Creating Current in a Marine Tank
Produce Strong, Variable Flow with a Return Pump and CLS
When attempting to create a biotope-specific tank where the physical characteristics are dominated by strong flow, more than a simple return pump is needed.
In order to replicate an Indo-Pacific nearshore reef in a 135-gallon aquarium, it is useful to know what physical forces create the natural habitat. This article will look at how current affects the reefs off Hoga Island in the Western Banda Sea and how the aquarist might recreate those dynamics in the marine aquarium using both an open and closed system.
The reefs around Hoga Island are known for their strong currents. The flow rate in the aquarium, like the flow rate on the reef itself, will influence the reef energetics and nutrient dynamics. To create strong currents consistent with the natural ecosystem, the aquarist needs to go beyond the often recommended reef tank return flow rate of 10 turnovers per hour. Because, as has previously been mentioned, the entire system of interconnected biotope-specific tanks holds around 230 gallons of water, a return pump rated to 5800 gallons per hour (GPH) is used in this set-up. This pump provides a flow rate of around 2400 GPH (when head pressure is factored in), resulting in just over a 10 times per hour turnover rate.
This flow is nothing close to the currents experienced on an actual reef off Hoga Island, however. To solve this problem, a closed loop system (CLS) was also installed. The CLS draws water from mid-tank by way of two one and one half inch intakes and then returns it to the tank (by way of an Oceans Motions 4-Way wavemaker) through four Omni Flex Nozzles (also made by Oceans Motions). The Oceans Motions 4-Way is capable of handling flow rates over 7500 GPH, which means that a fairly powerful pump can be used. To calculate which pump to use for the CLS, the same formula is used as was used when determining the return pump's size.
Once a sufficient flow through the tank has been accomplished through both the return pump (or the open system) and the CLS, the aquarist can then focus on the flow patterns. For the 135-gallon tank, a barrelling effect was created by mounting two of the CLS returns high on the back wall of the tank and directed down onto the rockwork. The other two CLS returns were mounted in the front bottom of the tank and directed back at the rockwork. The OM-4 causes the top back returns to operate simultaneously and then the bottom front returns to operate simultaneously, creating a rolling pattern such as is experienced on a shallow nearshore reef.
The combination of the open system’s return combined with the CLS creates flow somewhere in the range of 6000 GPH in the system. This means the entire system is turning over more than 20 times an hour. In the display tank, which is only 135 gallons, the current moves even faster relative to the tank's size. This recreates a very natural physical habitat for fish and invertebrates indigenous to a nearshore reef off the coast of Hoga Island.
Additional Resources:
- Read John Blatchford's article "The Coral Triangle - Wakatobi is a Marine Natinal Park South of Wallace’s Line"
- This is Part 7 in the Biotope-Based Marine Aquaria series. Read Part 6.
- Discuss this article here.
