A Simple Guide To Aquarium Auto Top-Offs


Automatic top-off systems are the best way to create a consistent water level in your aquarium. A consistent water level will stabilize your water parameters, providing a stable environment for your animals. An auto top-off will also save you time and make it easy to maintain your water level during a vacation. Added benefits include better protein skimmer performance and supplement dosing.

Here is a detailed list of the benefits of an auto top-off:
Increased Stability – Maintaining water levels is critical to maintaining your water parameters. When your water evaporates it causes many water parameters to change. Simply put, when the water evaporates there is less water and the same amount of everything else. This means that when water evaporates your calcium, ammonia, nitrate, phosphate, and salinity concentrations all increase. Adding an auto top-off can reduce these changes and provide a more stable environment for your animals.

Less Maintenance – Using an auto top-off is easier than manually replenishing water on a daily basis. When an average-sized reservoir is used most people will go a week before needing to refill the reservoir. A larger reservoir will allow you to go even longer between refills. This is great for aquarists who travel frequently.

Consistent Water Level – Some pieces of aquarium equipment, such as protein skimmers and surface skimmers, do not function well when the aquarium water level changes. Adding an auto top-off can ensure this equipment will function optimally.

Simple Supplementation – Auto top-offs can be used to automatically dose certain supplements. Simply add the additive to the top-off water and then small amounts of the additive will be added throughout the day. Some additives that work well with auto top-offs include Seachem Flourish Excel, Seachem Kalkwasser, and Brightwell Aquatics PhosPhatE.

Videos Demonstrating How an Auto Top-off Works: Which Auto Top-Off Should You Purchase?
The number one concern with auto top-offs is the failure to turn off. If this happens the salinity in your tank could drop significantly, causing harm to the animals in your tank. Water could spill onto the floors ruining your floors and possibly become an electrical hazard. Any additive added to the auto top-off would be overdosed. Additionally, you’ll want a unit that is low profile and low maintenance. With this in mind here are five of our favorites at different price points.

IceCap ATOs – The IceCap ATO EZ System is an easy-to-use pump and sensor combo that offers peace of mind when replenishing evaporated water into an aquarium. Its twin optical sensors extend the device’s life and reliability by limiting the frequent powering on and off of the refill pump. This system also includes a third (safety) sensor that provides another level of security to prevent overflows.

JBJ Nano ATO - The JBJ Nano ATO Advanced Auto-Top-Off System Is a successor to one of the most popular ATOs of all time. This simple and highly affordable unit comes in at half the price of some of the other ATOs and it has a very low profile sensor ideal for placing in small compartments of all-in-one nano aquariums such as the Coralife BioCube.

Tunze Water Level Controllers
The Tunze Osmolator 3155 is one of the safest ATOs available. It utilizes an electronic eye sensor to monitor water levels and a backup float switch sensor with an optional audible alarm. The controller protects the quiet metering pump from running dry and reports an empty storage tank. Two magnetic holders for sensors and multiple mounting brackets are included as well as a pump. LED indicator lights in the Osmolator will allow you to visually see if there are any issues with your top-off system. This ATO can be used with the Tunze Osmolator 3155 Water Level Controller Controlled Power Socket.

The Tunze Osmolator 3152 Nano Water Level Controller is the little brother of the Tunze Osmolator 3155 one of the industry’s most trusted automatic water top-off devices. Designed specifically for smaller aquariums, roughly 50 gallons and under, the Osmolator Nano 3152 is a slimmed-down version of the full-sized 3155.

The Tunze RO Water Controller 8555 is an automatic water level controller used in the collection container of the Tunze RO station. The controller is also suitable for other water tanks or can be connected to an automatic refill system. It consists of a controller, two sensors, a water valve, and a 12 V power supply unit. Depending on the use, the water valve can be replaced by switched socket outlet 3150.110 for mains operation.

Neptune Systems ATK V2 Automatic Top-Off Kit
The Neptune Systems ATK V2 Automatic Top-Off Kit integrates with the Neptune Apex Controllers or can be used by itself. It uses dual optical sensors and a backup float plus other features such as pump timeout to make sure the unit is super reliable. The ATK is a more expensive option, but one that is definitely worth it if you would like more features or already have an Apex Controller.