How Well is Your RO/DI System Really Working?

So you have a reef aquarium filled with stunning corals and invertebrates or you are running a fish only system. Either way, chances are that you’re using an RO/DI system to produce freshwater for topping off evaporation or mixing seawater. The question is though, how well is the system really working? In this article, I will explain what to look out for and how you can remove all doubt.

If you’ve already invested in a TDS monitor, then you’re able to monitor the TDS output of your system. Using one of these invaluable tools is one way to confirm your RO/DI system is functioning correctly. Although it is not an exhaustive method of confirming your system is in tip-top shape. A TDS reading of 0ppm does not mean your RO/DI system is producing 100% pure water.

Let me explain. Like most pieces of equipment in the reef aquarium hobby, RO/DI systems need to be maintained. They house a sediment filter that gets clogged up over time. Once this happens, it can play havoc with the pressure in your system. Low pressure will degrade your RO membranes rejection rate. When carbon filters become depleted and are not replaced in time, they can start allowing chloramines and chlorine to reach your RO membranes, resulting in oxidation of your RO membrane, causing permanent damage. RO membranes also need to be replaced and if they are not, their rejection rate collapses, allowing high TDS water through to your DI resin, causing the resin to become rapidly depleted. Any number of these scenarios means your system is failing and unfortunately, your TDS monitor will not always alert you to this fact.

A seemingly well-running RO/DI system can produce 0ppm TDS water. However, there may be some contaminants remaining that your TDS monitor is just not capable of measuring. This is because these types of TDS monitors work by measuring electrical conductivity and not all contaminants contribute to conductivity. Most TDS meters have an accuracy rating of ±2%, this means that some remaining contaminants can fly beneath the radar.

Whilst there are a number of contaminants that can get past a TDS monitor without detection, one of the most common is silicates, which are responsible for diatom blooms in the reef aquarium. This is because silicates are one of the most resilient minerals when it comes to filtration, even bypassing DI (deionisation) resin. The reason for this is due to the fact that they are not always charged negatively or positively, allowing it to pass through DI resin without being attracted to either anion or cation resins.

What you may not know is that the modern reef aquarium hobbyist is able to remove all doubt and be sure of their RO/DI system’s performance. Using the exact same ICP-OES (inductively coupled plasma optical emission spectroscopy) testing that has been made available by a number of companies internationally, you can have your RO/DI water tested for peace of mind.

ATI provides a full-scale ICP-OES testing service for your reef aquarium. In addition, they also provide a 3rd vial for a sample of your RO/DI water. They will test your RO/DI water for both major and minor trace elements, using ICP-OES, down to the parts-per-billion level. This is not something that your TDS monitor is capable of and you may be very surprised by the results.

The elements that they will test for are as follows:

As the Australian distributor for ATI, Reef Secrets Aquariums in QLD stock the ATI ICP-OES test kits. So if you want to be sure, grab a test kit and get the answers. I believe everyone with an RO/DI system should have one of these tests done at least once a year. We all test our aquariums and we know that testing is one of the major keys to success in the reefing hobby, so why wouldn’t you test your RO/DI before using it in your aquarium?