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Electronic Monitors – Serious Equipment for Serious Aquarists

Hey everyone, Justin here. Working on the sales floor, I answer questions from customers each day about testing equipment. which to use, how accurate and easy the kits are, and lots of other specifics. Today I’d like to shed a little light on testing and monitoring tools, especially the electronic monitoring tools available to aquarists. There are several methods of testing the water conditions in your aquarium, including titration tests and test strips. Less frequently used are the electronic monitors. Electronic Monitors are a different way of testing your aquarium parameters quickly, easily, and accurately. Instead of using a Titration kit (liquid) or paper strips (litmus), Electronic sensors can detect specific components of your aquarium water, such as: pH, Nitrate, Calcium, Salinity, and Dissolved oxygen, in a matter of seconds. If calibrated and cared for correctly, your monitor can provide constant testing with pinpoint accuracy, which can be a real benefit, especially in complicated systems. Large systems can be huge investments in livestock alone, and pristine water conditions protect your investment.

How they work

There are many monitors/controllers available. Most of them work in a very similar manner and have a similar function as others, but each is designed to give you the most accurate readings possible for what you’re monitoring. Monitors and controllers have the ability to automate some situations faced by beginner and expert aquarium hobbyists alike, and may alert you to situations with chemistry issues, ultimately helping you to avoid bigger problems in the tank.

Monitors and/or controllers may be used with separate equipment to reach exact water parameters. CO2 controllers will monitor your pH and add CO2 gas into your aquarium by controlling your CO2 system’s solenoid valve for any heavily planted aquarium. CO2 systems are more efficient when used with a pH controller. The solenoid valve of the CO2 system is plugged into the pH/CO2 controller and will inject CO2 into the aquarium when the pH rises above a set point. The same set-up should also be used for Calcium reactors to ensure efficient calcium dosing in any reef aquarium. A Calcium reactor works similar to the CO2 system, except as the pH drops, calcium is introduced into the aquarium.  ORP controllers and REDOX monitors should be used when dosing Ozone in your aquarium. They can safely control Ozone dosing in very large or heavily stocked aquariums to ensure the quick breakdown of wastes.  Testing with these monitors is simple, inexpensive (though your initial investment is more) and incredibly accurate. Whenever purchasing a RODI unit it is important to purchase a TDS meter or pen. TDS meters will give you an indication when to change the membrane(s) and cartridges in your R/OD/I unit. The TDS meters measure the total dissolved solids going into and coming out of the RODI unit. Many of the TDS pens will monitor multiple parameters such as pH, temperature, and sometimes salinity. The mini TDS meters work inline with the RODI unit while the pens are hand held and work independently.

PH monitorElectronic monitors use electrodes or probes to give you readings. The probes contain a small, super thin glass bead to allow the diffusion of molecules across the surface of the glass, this called the sensing glass. The glass ball is used primarily in older probes but are still present today. These glass bulbs are incredibly fragile so they need to handled carefully and cleaned regularly. The electrodes use very small electric sensors built into the tip of the electrode, this is called the reference junction. Electrodes last longer and are generally less expensive to produce. There may also be copper plated wire sensors used in some more advanced, industrial monitors.


Calibration is a critical part of all monitors. All monitors will work without being calibrated but they will not be accurate. Calibration is usually done with 2-3 different values to determine a reference point. For example, pH is usually calibrated with a 4.01 buffered solution, 7.01 buffered solutions, and 10.01 buffered solution. This is to ensure accuracy over a wide range of values. Calcium monitors are usually calibrated with a 100 ppm solution and a 1000 ppm solution. Nitrate monitors are calibrated with several solutions up to and including 100 ppm. Salinity monitors are calibrated using 0 ppt up to (in some cases) 50 ppt.

Cleaning the probes or electrode regularly will extend the life of the probe and will ensure accuracy. Cleaning is incredibly simple, a rinse with RODI water will clean any of the sample water off of the probes. For cleaning continuous use probes, it is important to soak the probes in a 1:10 vinegar to water solution to remove any mineral/algae/calcium build-up. This should be done monthly in freshwater aquariums and bi-weekly in saltwater aquariums. After a bath in the cleaning solution, it is necessary to rinse the probe tip with RODI water. We also sell a buffered rinse solution.

When not using continuous testing, it is necessary to store the probes. Probes and electrodes should be stored in an upright position in a buffered solution. Usually the probes are stored in a neutral solution (pH) or at values of 0 (Calcium, Nitrate, Phosphate, etc). It is very important that the probes do not dry out as the glass balls will crack when re-saturated and the electrodes will malfunction.

Though the initial cost of electronic monitors and controllers is significant, properly used and maintained, these tools can become invaluable to serious aquarium keepers. If you have any questions abotu the benefits or function of monitors or controllers, please comment, call or visit, our sales staff will be happy to assist you.




  1. avatar

    Hi dear
    I read your text about effect of ozone on aquarium in salt water.
    I have questiones about what are the effects of ozone on aquarium in freshwater?
    And measure of level and harmful ORP for fish in freshwater?
    What is the damage range for freshwater fishes??
    Best regard.
    Hadi mahmoudi.

  2. avatar

    Hello Hadi, I would recommend reading our blog article “Using Ozone in the Home Aquarium“. This article has information on recommended dosing rates and usages.

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