DI Cartridge - Which One? How Many?

We all want ultra-pure, ZERO TDS, water for our aquariums. With several Deionization Filter options available, it can be confusing which cartridge(s) you should use. And how many? 

For the majority of hobbyists, a single Standard DI Filter Cartridge works great! Our standard DI filter uses a mix-bed resin that is made in the USA and is nuclear-grade, virgin resin (not regenerated). Nuclear-grade resin is the highest grade DI resin available and is capable of delivering ultra-pure water that measures 18 ohm resistivity. The Standard DI Filter comes in a refillable cartridge so you can save money by purchasing refill resin once time is due. The resin also changes color to an amber/orange color once it is exhausted, so you know when a replacement is needed.  

Our XL DI Cartridge offers the best replacement cartridge value. This larger DI filter cartridge holds 18% more resin for just $1.00 more. Due to the cartridge design, the XL cartridge is not refillable.  

For hobbyists that have higher silicate/phosphate levels in their water source, or for those that have more-frequent algae issues in their aquariums, the Silicate Blaster DI Cartridge is a great option. This cartridge contains more of the anion DI resin to help remove as much of the silicate/phosphate as possible.  

Our DI filters will provide ultra-pure, zero TDS, water. Once the DI filter becomes exhausted, the TDS will start creeping upwards. We typically recommend replacing the DI cartridge once the TDS reads 2-5ppm. 


In most applications, a single DI cartridge is sufficient and does an excellent job providing pure water for your aquarium. However, running 2 or 3 DI filters will give you cleaner water and can actually save you money.  In a double DI filter setup, two mix-bed DI cartridges are used in series. The first DI cartridge does the majority of the work while the second DI cartridge is the back-up that catches any impurities missed by the first cartridge. Once the first DI cartridge becomes exhausted, you simply move the second DI cartridge to the first slot and add the new DI cartridge in the second slot. You still replace just one DI cartridge at a time, but this allows you to completely exhaust the first DI cartridge without worrying about bypass or producing poor quality water. End result is cleaner water that is always zero TDS (even as the first DI cartridge becomes fully exhausted as water is passing through 2 DI cartridges) and lower cost in the long run as you are able to fully exhaust each DI cartridge before having to replace it. 

Upgrading your system to incorporate more DI filters is also super easy with our add-on kits.


For advanced hobbyists or those with larger aquariums, a third DI filter can make the system perform even better and more economical. In a triple DI filter set up, the mix-bed resin is split into two separate stages: cation (positive ion) stage and anion (negative ion) stage. The 3rd stage remains as a mix-bed DI stage. Water first passes through the Cation resin where positive ions like calcium, copper and magnesium ions are removed. It then passes through the Anion resin where negative ions like silicates and phosphates are removed. Having separate cartridges for each resin allows the resin to work more efficiently. Additionally, Cation is typically used up twice as quickly as the Anion. The separate cartridges allow you to replace only the resin that becomes exhausted; saving you money. As with the double DI setup, the last mix-bed DI cartridge is the catch-all for anything missed. 


With all the different options available, finding the ‘best’ DI filter setup can be confusing. Fortunately, any DI setup with a high-quality resin will give you excellent water for your aquarium. Knowing the advantages of each option gives you the tool to pick out the perfect DI filter setup to suit your needs. 

At AquaFX, we offer better filter, better service! If you need help choosing a DI filter, please do not hesitate to email us or give us a call.

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