Eshopps Fusion Flow FF-75 Sump Upgrade: Dual-Sump Setup for a 125-Gallon Saltwater Tank

Introduction

Upgrading a sump system on an established 125-gallon saltwater tank requires careful planning when space is limited. A dual-sump approach using the Eshopps Fusion Flow FF-75 alongside an original Eshopps sump provides independent filtration paths while respecting the physical constraints of the tank stand.

Tank Layout and Space Constraints

The 125-gallon tank is 6 feet long with two overflow drains, one on the right side and one on the left. The stand has a center brace that limits the width available beneath each side to exactly 15 inches, making it impossible to fit a single large sump underneath. Rather than removing the center brace and risking structural failure, the dual-sump strategy keeps both the original sump and adds a new Eshopps Fusion Flow FF-75 to handle the increased water volume and flow demands.

The original sump, which has been in service for eight years, handles the right-side overflow and includes a protein skimmer. The new Fusion Flow FF-75 receives water from the left-side overflow, providing dedicated mechanical filtration for that side of the tank.

Mechanical Filtration Setup

The Eshopps Fusion Flow FF-75 holds 14 gallons, which is sufficient for this application. Rather than using the included Bio-Lux ceramic columns, custom filter pads are layered inside the slide-out tray. Each pad consists of white foam approximately a quarter-inch thick sandwiched between soft gray cloth mesh fabric. Two pads are stacked together, then topped with two layers of blue pond filtration foam. This configuration provides effective mechanical filtration while remaining easy to rinse and maintain.

Water flows from the overflow into the sump, passes through the foam layers via the drip plate, and then returns to the tank. The slide-out tray design makes media replacement straightforward, allowing the foam to be removed and rinsed without breaking down the entire system.

Balancing Flow Between Two Sumps

Both sumps use a Rio Plus 2500 pump to return water to the tank. However, because the original sump is larger than the Fusion Flow FF-75, a balancing act is necessary. If both pumps operated at full capacity, the larger sump would retain more water while the smaller sump would be drained too quickly.

The Rio Plus 2500 pumps include integrated flow control valves that allow fine-tuning of the water suction rate. By adjusting the valve on the Fusion Flow FF-75 pump to approximately 11 o’clock (rather than fully open at 12 o’clock), the suction rate is reduced just enough to match the smaller sump’s capacity. After about an hour of adjustment, the water levels stabilized perfectly, and over the following 10 minutes, the water line did not move even a millimeter.

Tank Configuration and Rock Layout

The tank currently contains no fish, as they were temporarily relocated while the rock structure was replaced. The original live rock was removed and replaced with dry rock that is gradually developing a natural caramel color. Only one piece of original live rock remains, along with rock branch structures and a single piece of live rock hosting a Duncan coral.

The sandy substrate is approximately three years old and continues to support beneficial bacteria. The fish will be returned to the tank in a couple of weeks once the new rock structure is fully established. Additional rock pieces are planned to create bridge structures that allow water flow and provide swimming passages for the fish.

Maintenance and Media Replacement

The mechanical filtration pads in the Fusion Flow FF-75 are changed once per week, keeping the water polished and clear. The protein skimmer in the original sump also includes mechanical filtration foam that is replaced on the same weekly schedule. This regular maintenance keeps both sumps functioning optimally and prevents the buildup of detritus.

Conclusion

The dual-sump configuration using the Eshopps Fusion Flow FF-75 and the original Eshopps sump provides a practical solution for a 125-gallon tank with space constraints. The Fusion Flow FF-75’s compact 14-gallon capacity, combined with custom mechanical filtration and the Rio Plus 2500 pump’s flow control valve, creates a stable, low-maintenance system that keeps water quality high while respecting the physical limitations of the tank stand.