Ten to fifteen years ago, in the “dark ages” of aquaria, hobbyists had few options when it came to aquarium automation.

The amount of lighting my aquariums received back then depended on when I remembered to turn the lights on and off. Some days my tanks would receive as little as two hours per day; other days, up to fourteen hours.

This kind of inconsistency will simply not do in today’s reef aquaria.

Fortunately, we now have a veritable arsenal of controllers and timers available to us. From a simple light timer to the most advanced all-in-one monitor/controller, these innovations in aquarium technology can save us time, money and often provide more accurate monitoring than traditional testing methods.

1. Lighting

The most commonly controlled (or automated) devices in aquariums are lights.

A simple mechanical timer is the easiest way to turn aquarium lights on and off to create a solar cycle. Adding (lunar) moonlights to this setup will provide a full 24-hour effect.

More advanced timers take this cycle a step further. By altering start and stop times, seasonal changes can be recreated … including the 28-day lunar cycle and the 365-day solar cycle. In fact, many hobbyists and professionals credit this natural cycle for stimulating spawning in corals and reef fish.

2. Temperature

The temperature of a captive reef is the most important variable to monitor and control. In the wild, temperatures do not vary more than a degree or two over the course of a year. Large fluctuations in temperature can stress aquarium inhabitants, potentially leading to sickness and even death.

Most heaters and chillers nowadays are equipped with single-stage controllers that turn on and off the devices as needed. Of course, a dual-stage temperature controller is an even better option. Dual-stage controllers monitor and control heaters and chillers (or fans) simultaneously to allow even more precise control.

3. pH

The power of Hydrogen is a calculation between the ratio of Hydrogen ions (H+) and Hydroxide ions (OH−). It measures the acidity or basicity of a solution on a scale of 1 to 14, with a value of 7 being neutral. Anything below 7 is acidic; anything above is basic.

Proper pH levels are vital to the health of a reef aquarium and its inhabitants. It is best to keep your pH between 8.1 and 8.4.

Understanding pH can also make you a better reef keeper. For instance, you can use this insight to properly adjust the output of a calcium reactor. This is actually why more advanced pH controllers include 2 pH probes: one to monitor the main display tank, the other to control a reactor.

4. ORP

Oxidation-Reduction Potential is a measurement of how well your aquarium system oxidizes contaminants. In short, how effective is your filtration?

Natural sea water has an ORP (measured in milliVolts, mV) between 300 and 450, so you should strive to maintain these values. Oxygen can be depleted if ORP gets too low and algae blooms often take over. If ORP gets too high, the flesh of your aquarium inhabitants can quite literally burn, starting with the most sensitive areas (gills, eyes, etc.).

The easiest way to maintain ORP is make sure your filtration is adequate and do not overfeed. Should this not be enough, an ORP controller can monitor and control oxidizing equipment like a UV sterilizer or ozone generator.

5. Water Circulation

There are countless benefits to having good water flow in your aquarium.

Adequate water flow should circulate aquarium water to and from filtration equipment, limit the amount of detritus that settles at the bottom, oxygenate water, remove excess nutrients and reduce stress levels in many fish.

Controllers can create a random flow to mimic the ocean. Many can also be programmed to recreate tidal and wave patterns that match specific ecosystems. Creating the most natural environment possible for your animals is responsible reef keeping.

Which controller is right for you?

Good question. The answer, of course, depends on what you want/need it to do.

The chart accompanying this article compares some of the better all-in-one controllers currently available and may help narrow your selection. I have personally used five of the six controllers compared, with the exception being the ELOS Biotopus. It’s still out of my price range (for now) but I’ve heard it’s worth every penny. Of the remaining five, each has its strong points as well as a room for improvement. All are easy to program, taking only minutes to get accustomed to the setup instruction. Here are my thoughts on each:

  • AquaController Jr.
    A great entry-level controller. It is capable of using 40 timers on 12 outlets along with monitoring pH and temperature. Since this is an entry-level controller, the AC Jr. cannot monitor ORP.
  • AquaController III
    The AC III is a step up from the AC Jr. It is capable of controlling multiple aquariums, utilizing 100 timers with a maximum of 48 outlets. It monitors and controls aquarium temperature, pH and ORP.The AC III also has an Ethernet port for direct connection to the Internet. This useful feature gives you the freedom to monitor and control your aquariums from anywhere there is a web connection. There is even an AC III iPhone app available so you can control your tanks from a mobile device.
  • AquaController III Pro
    The AC III is bigger and better than its little brothers. It has all the capabilities of the AC III, plus salinity and dissolved Oxygen control. It runs up to 80 outlets using 160 timers.
  • Reef Keeper Lite
    The RKL is entering the market as of this writing. It is a competitively priced entry-level controller from Digital Aquatics. Temperature control is built in and pH and ORP may be added by way of an SL1 module. As a low priced entry-level device, it is limited to 4 modules (PC4s, SL1s and MLCs).
  • Reef Keeper Elite
    For more flexibility than the RKL, try the RKE. It monitors/controls temperature, pH, ORP, salinity and dissolved Oxygen. The RKE runs up to 63 timers and 63 modules, giving the user a seemingly endless number of options. The RKE and the RKL can both be flush-mounted into a stand to create a sleek, modern look.
Elos Biotopus
Display Size 2x16 LCD 2x16 LCD 4x20 LCD 2X16 LCD 128x64 Graphical 4x20 LCD
I/O Ports 1 2 4 No Yes (5 per SL1) 1
PC Connection RS232 RS232/Built-in Ethernet RS232/Built-in Ethernet USB USB RS232
Temp Control Yes Yes Yes Yes Yes Yes
pH Control Yes Yes Yes Yes Yes Yes
ORP Control No Yes Yes Yes Yes Yes
Salinity Control No No Yes No Yes Yes
Dissolved Oxygen
No No Yes No Yes No
Float Switch (Qty) 1 up to 2 up to 4 2 per SL1 module 2 per SL1 module 1
Yes (A/V) Yes (A/V) Yes (A/V) Yes (A/V) Yes (A/V) Yes (A/V)
Max # of Timers 40 100 160 16 63 43
Ethernet Port No Yes Yes No Yes (optional NET module) No
Web Server Control Yes (with the full version of AquaNotes Yes Yes No Possible in the future No
Custom Design
HTML Pages
No Yes Yes No Possible in the future No
Email Alarms Yes (with the full version of AquaNotes Yes Yes No No Yes (via SMS)
Power Failure Alarm No Yes (Audible or Email) Yes (Audible or Email) No No Yes (via SMS)
Internal Battery
Yes Yes Yes Yes Yes Yes
Multi Aquarium
No Yes Yes Yes Yes No
Password Protection
Yes Yes Yes Yes Yes Yes
Seasonal Programs Yes Yes Yes No No Yes
Moon Simulation Yes Yes Yes Yes (with optional MLC) Yes (with optional MLC) Yes
Wave Generation
Yes Yes Yes Yes Yes Yes
Night Mode Programmable Programmable Programmable Yes Yes Programmable
Alternate Power
No Yes Yes No No No
Optional Expansion
None up to 24 probes and 42 digital inputs up to 24 probes and 42 digital inputs 4 (total expansion modules) 63 (total expansion modules) 512 single power plugs can be chained + 2 I/O Ports
Available Power
Bar Sizes
8/4/4 Heavy Duty (all 115VAC) and 220V Expansion 8/4/4 Heavy Duty (all 115VAC) and 220V Expansion 8/4/4 Heavy Duty (all 115VAC) and 220V Expansion 4 Plug 115V With built in IntellaStrip Auto Overload Shutdown 4 Plug 115V With built in IntellaStrip Auto Overload Shutdown 6 Plug 115V and 220V
Power Strip Max Qty 3 6 10 4 63 2 or 3 depending on type
Power Strip
Manual Override
No No No Yes Yes Yes
Power Strip
Max Amperage
15 Amps 15 Amps 15 Amps 15 Amps 15 Amps 15 Amps
Variable Pump
Speed Capable
Yes (optional) Yes (optional) Yes (optional) No No No
Feed Mode Yes Yes Yes Yes Yes Yes
Soft Start Yes with DC8 Yes with DC8 Yes with DC8 Yes Yes ---
(H x W x D)
2.75" x 4.60" x 1.00" 3.70" x 5.75" x 1.10" 4.0" x 7.50" x 1.10" 2.8" x 3.9" x .6" 3.46" x 4.44" x 0.85" 5.25" x 8.25" x 1"
Starter Kit Includes 1 x Head Unit

1 x Temp Probe

1 x Head Unit

1 x Temp Probe

1 x Head Unit Level 1

1 x Head unit

1 x PC4(4 outlets)

1 x Temp Probe

1 x Head Unit

2 x PC4(8 outlets total)

1 x SL1

1 x Programming Dongle

1 x pH Probe Kit

1 x Temp Probe

1 x Head Unit

1 x Multiplug (5 outlets + Osmocontroller)

1 x pH Probe

1 x Temp Probe