Simplicity Easy-Fill ATO Reservoir

The Simplicity Easy-Fill ATO Reservoir gives your auto top-off system a clean, sealed supply of fresh water so your aquarium's water level and salinity stay stable between refills. A patent-pending wide-mouth lid folds open into a built-in funnel with an integrated splash guard, letting you pour top-off water in from the front of the cabinet without pulling the reservoir out or making a mess. Choose the 5 Gallon for nano and mid-size tanks or the 10 Gallon for larger systems and longer intervals between fills. Browse more saltwater and freshwater gear.

Why You'll Like It

• Front-fill funnel lid: the removable wide-mouth lid converts into a funnel, so you refill from the front, ideal for tight in-cabinet spaces.
• Integrated splash guard: keeps refills clean and spill-free.
• Sealed against evaporation and dust: protects your top-off water from contaminants and keeps salinity consistent.
• Universal fit: works with any auto top-off system, float switch, or optical sensor.
• Cabinet-friendly footprint: engineered to slide into standard aquarium stands.
• See-through water level: durable black base with a clear front panel so you can check your reserve at a glance.

How It Works

Fill the reservoir with RO/DI or top-off water, drop in your ATO system's pump and float sensor, and the reservoir feeds fresh water into your sump or tank as it evaporates. The wide-mouth funnel lid means topping the reservoir back up takes seconds, with no lifting or siphoning required.

Choose Your Size

Which Size Is Right for You?

The 5 Gallon suits nano and mid-size reef or freshwater tanks and fits most compact stands, needing about 20 inches of vertical clearance to open the lid. The 10 Gallon holds twice the water for larger displays or setups with higher evaporation, stretching the time between refills. Make sure your cabinet has at least 26.5 inches of clearance so the lid can swing open.

Specifications

• Brand: Simplicity
• Type: Auto top-off water reservoir
• Capacity: 5 gallons (19 L) or 10 gallons (38 L)
• Material: Durable molded plastic, black base with clear front panel
• Lid: Removable wide-mouth funnel lid with integrated splash guard (patent pending)
• Compatibility: Any auto top-off controller, pump, float switch, or optical sensor
• Water type: Freshwater and saltwater / reef aquariums

Recommended Pairings

• Auto top-off controllers and pumps to automate your refills
• Simplicity DC Return Pump for your sump
• Water care and maintenance supplies

Frequently Asked Questions

Does this come with an ATO pump or sensor? No. The reservoir is the water container. It is built to work with any auto top-off system, so you can add or reuse your preferred controller, pump, and float or optical sensor.

Can I use it on a freshwater tank? Yes. It works for both freshwater and saltwater. For reef and saltwater tanks, fill it with RO/DI water to keep salinity stable as water evaporates.

Why the funnel lid? The wide-mouth lid folds open into a funnel with a splash guard so you can refill the reservoir from the front of your cabinet without removing it, a real help in tight aquarium stands.

Will it fit in my stand? Both sizes have a slim footprint built for standard aquarium stands. Check the clearance figures above, 20 inches for the 5 Gallon and 26.5 inches for the 10 Gallon, so the lid has room to open.