Salinity is one of the most important parameters to maintain in a saltwater aquarium. Throughout the day water evaporates from your tank, but it’s only the freshwater that evaporates, and the salt is left behind.
To maintain proper salinity you can manually add freshwater into your tank, or you can take the automatic approach and install and automatic top off system.
Auto Top Off systems or ATO as they are referred to essentially drip feed your tank with freshwater as needed so the salinity level remains stable. No need to worry about your salinity creeping up, just keep your auto top off reservoir full of fresh clean RODI water, and you’re all ready to go.
When picking an automatic top off you can either choose a gravity-fed or fully automated electronic device. Below are some of the best options for choosing an ATO for your saltwater aquarium.
Automatic Top Off Device
- Auto Aqua Micro ATO
We’ve seen many iterations of the optical water sensor auto top off device, starting with the original Auto Aqua Smart ATO Micro. The optical sensor devices were a revolution in auto top-off technology and with no moving parts, there is little room for failure.
- Neptune System Auto Top Off Kit
The Neptune Systems ATKv2 (Automatic Top-off Kit) is a simple, standalone, and complete solution for replacing water lost to evaporation. The Neptune auto top off works with or without the apex controller. The ATKv2 system comes with a strong magnetic fastener which holds both the mechanical float valve, and a pair of optical float switches.
- TUNZE Osmolator Universal
The Tunze Osmolator is the original auto top off system for marine aquariums. The Osmolator has extra security built into the device, and should the primary optic sensor fail, a safety float switch shuts the unit off and sounds an alarm. Even if that fails safety circuitry shuts off the pump after 10 minutes.
- Hydor Smart Level
Smart Level is a fully electronic water level controller designed by Hydor.
Smart Level technology reduces the problems related to limescale deposits, bacterial film, and wave action, which ensures the continuous, safe, and regular functioning of the Smart Level control.
- Innovative Marine Hydrofill TI
The HydroFill Ti ATO uses water’s conductive properties to complete a low voltage circuit and cause a control relay to actuate and replenish water as it evaporates. Customize your own “High and Low” set points to prevent constant On/Off cycling prone to single sensor design.
Gravity Fed System
- Aqua Medic Refill Fix Nano ATO
Refill Fix is a low tech device from Aqua Medic that provides a small amount of water which is lost due to evaporation. The simple gravity drip device can be used with any commercially available PET beverage bottles up to 2 liters too easily and simply replenish evaporated water.
- Eshopps Aqua Float and Reservoir
The Eshopps aqua float valve sits inside a water reservoir either a sump or other container and when the water level gets high enough to float the switch the water turns off simple as that. The Eshopps float valve can hang-on or can be drilled into the side of a vat. The float valve attaches to a water source via a 1/4″ tubing to replenish evaporated aquarium water.
Auto Top Off Resevoir
- Pro Clear Aquatics Auto Top Off Reservoir
An auto top off reservoir is required for all ATO devices as it holds a quantity of freshwater used to top up the aquarium. Pro Clear Aquatics makes an acrylic version in 2 sizes, 6 gallon and 10 gallon. Both the 6 and 10 gallon models features two holes in the top. One for your pumps power cord and the other for your tubing to your sump.