With everyone using different amounts of water and every city and every well having different water quality, it is difficult to tell someone when they should change the filter cartridges on their RO or RO/DI system. One hobbyist may only need to change their filters once a year, while another may need to change theirs monthly.
For those that like things as simple as possible, we recommend changing out all the bottom filters (sediment filter, carbon filter and DI filter) whenever the DI filter is exhausted and the resin has changed color. The color change will start from the bottom of the cartridge and work its way up to the top. When it is about 1” from the top, it is time. DO NOT wait until the cartridge has fully changed color. While this method does not maximize the usable life of the sediment and carbon filters, the filters are relatively inexpensive and this is an easy way to make sure everything runs optimally and you continue to get pure water for your aquarium.
For most hobbyists, the RO membrane is typically good for 1-2 years. When you notice that your DI filter is changing color more quickly than usual, it is probably time to change out the RO membrane as it is not working as effectively anymore.
For more-advanced hobbyists, coral farmers or aquarium stores that would like to know more-precisely when to change out their filters, we recommend the following guidelines:
1. Sediment filter - as sediment filters become clogged, water pressure will start to drop. If you do not have a pressure gauge on your RO/DI system, you can add one of our pressure gauge kits to monitor the system pressure. Replace the sentiment filter whenever you notice a pressure drop of 5PSI.
2. Carbon Filter(s) - the most important job of the carbon filter is to remove Chlorine (or Chloramines if present) as chlorine and Chloramines can quickly damage the RO membrane. Carbon filters are relatively inexpensive so changing it out whenever you change your DI filter is good, and cheap, insurance for your RO membrane and your aquarium. If you do not make water frequently, we do still recommend changing out the carbon filter at least once a year.
In cases where Chloramines is present, the carbon filters are even more crucial in ensuring no toxic ammonia makes its way to your aquarium and help your DI filter last as long as possible.
For hobbyists or stores that use a lot of water, especially those with large carbon towers, a more-accurate method of knowing when to change out the carbon filter can help to save a lot of money and help to ensure the RO/DI system is operating efficiently and effectively. The easiest method for testing is to test for Total Chlorine in your waste water. Use a low-range Total Chlorine Test Kit (such as the LaMotte 2693LR Test Strips or Hanna Total Chlorine Checker) to test for Total Chlorine in your waste water after allowing the RO/DI System to run for 30 minutes. If the total chlorine level measures 0.5ppm or higher, it is time to replace your carbon.
3. Deionization Filter / Resin - it is important to replace the DI filter (or resin) in a timely manner as it is what brings the TDS down to zero: making sure the RO/DI water you are using for your aquarium is as pure as possible. The color-change resin in the filters offers a good visual estimate on when to change the filter. As a general rule, a DI Filter will process 500 gallons of water at 10ppm, 250 gallons at 20ppm, 100 gallons at 50ppm. The lower the TDS from the RO portion of your RO/DI system, the longer the DI filter will last.