Changing your RO/DI filters is one of those maintenance tasks that are super easy, but so many of us put it off for far too long.  Failing to change your RO/DI system's filter cartridges can lead to harmful and/or toxic contaminants finding their way into your display aquarium.  By the time you realize the contaminants are in your tank, it's just too late. So the first step in being successful with filter maintenance is to understand how to monitor the individual filters so you know exactly when they should be changed out.  

READ ARTICLE: How To Monitor Your RO/DI Filters & When To Change Them

Once you know how to monitor the cartridges, swapping them out is simple. As Ryan likes to say - "The easier it is to do something, the less likely you are to neglect it." 

Gather the materials you need first and be sure to grab a towel. You will spill some water and exactly how much water you spill depends on how careful you are. Having a simple 5-gallon bucket helps alleviate some of this mess. The filter wrench is used to unscrew the stubborn canisters and then, of course, your new filter cartridges.

Ball valve position

Step 1 - Turn off the source water

Make sure that the water is off at the source. If you have a ball valve before your RO/DI system, just turn that off.  Otherwise, you need to turn off the source of the water from coming into your RO/DI system. 

  • Garden Hose: turn off the garden hose valve
  • Copper Pipe or saddle valve: turn off the valve connected to the pipe
  • Faucet: turn off the faucet

If you have the unit hooked up to a float valve and the valve is closed, the RO/DI system will be pressurized. You can also trap pressure in the system if you have a ball valve on the output side of the RO/DI system that is closed. Before removing the canister or disconnecting any tubing, you must relieve the pressure in your RO/DI system. 

Step 2 - Relieve pressure in the system

If your system has a float valve or ball valve on the output side of the unit that was closed at the time you turned off the water, the system may still be under pressure. Simply open the valve on the output side to release the pressure. It should take no more than 30 seconds for the pressure to escape completely.  It is then safe to close the valve again and proceed with changing your filters. 

RO/DI Filter Stages

Step 4 - ID the filter canisters and cartridges

It is important to put the right filter in the right canister. Ideally, each of your filter canisters is labeled so it's just a matter of aligning your new filter cartridges to the right labeled canister. The BRS RO/DI systems are plumbed as shown above. If you're not using a BRS RO/DI system, be sure to verify which cartridge goes into which canister.  When removing the old filter cartridges, it's pretty easy to tell the difference based on the appearance of the cartridge alone. 

Always work one by one in the following order. 

  1. Sediment
  2. Carbon
  3. Deionization or DI

Using a canister wrench

Step 3 – Replace Sediment & Carbon Filters

After you have identified the correct filters and their appropriate canisters, it's time to start working on the RO/DI system using a filter wrench. 

  1. place the filter wrench on the canister. The wrench slides on from the bottom and you want to slide the wrench as far up the canister as you can. The notches in the wrench will catch on the ridges of the canister as you rotate the wrench. Assuming you are looking at the unit from the front you should start off with the handle of the wrench rotated as far to your right as possible. The old adage “lefty loosy - righty tighty” applies 
  2. Next rotate the wrench to the left. Often a half of a turn with the wrench is all you need to get the canister loose.
  3. Grab the canister on the very bottom with your hand, proceed to twist it off completely.  
  4. Once the canister is removed, take it over to the bucket. The canister will be full of water and the old filter cartridge should be inside as well.
  5. Remove the old cartridge and replace it with the new one. The new cartridge should be vertical and neither the sediment filter nor the carbon blocks have a correct orientation. There is no top or bottom with either.
  6. Before placing the canister back onto the RO/DI unit, double-check and make sure the o-ring is properly seated in the canister. It should lay into a groove about an inch down from the top and not have any wrinkles in it.
  7. Thread the canister back onto the RO/DI system by hand until it is snug. Only use the wrench for the final turn and snug it up to hand tight. Do not overtighten the canisters.

The process is identical for all of your pre-filters (sediment filters and carbon blocks). Just repeat the steps for all of your prefilters until you have changed them all out. 

Changing DI Resin

Step 4 – Change your DI resin

The process for installing and removing the DI resin canister is the same but changing the DI media itself is a different process. You will either have a refillable DI resin cartridge or you will have a pre-packed filled DI cartridge.

Pre-packed Filled DI Resin Cartridge

  1. Remove the old DI cartridge as described above.
  2. Replace the new cartridge in the correct position.
  3. Reference the arrow located on the side of the new DI filter cartridge which should be pointing up. The position of your DI cartridge is important. 
  4. Screw the canister back onto the RO/DI System and you're done!

Refillable DI Resin Cartridge

If you're using a refillable DI cartridge, the DI resin will be loose media.  You need to remove the old media from the existing cartridge, then fill it with new DI resin media and pack it tightly.  

  1. Remove the canister and old DI cartridge as described above.
  2. Take the old DI cartridge, unscrew the cap, and set the cap aside. Be careful to not lose the cap or sponge that is inside. 
  3. Dump the old DI resin media into the trash. 
  4. Once it is empty, fill it with new DI resin media to about 25% full.  
  5. Tap the cartridge on your work surface 15-20x to settle the resin in as much as possible.
  6. Fill to about 50% full
  7. Tap the cartridge on your work surface 15-20x to settle the resin in as much as possible.
  8. Proceed with the process until the DI cartridge is completely full/overflowing with resin. The DI resin must be packed tightly or else it will not function correctly. 
  9. Once full, use your fingertip to draw a circle around the top edge of the resin to help remove any resin from the threads. Wipe the threads to be clean of any beads of resin.
  10. Place the foam ring on the resin, then push down on the sponge and screw on the cap. 
  11. Insert into the canister and screw it back onto your RO/DI System.

You're are all done! With new RO filters, it is best to rinse them before collecting any RO/DI water.  Turn on your source water then open your flush valve for 60 seconds to flush the sediment and carbon filters. Close the flush valve, and let the DI produce a gallon or two of water before collecting RO/DI water for use in your aquarium.  

In most cases, you will be performing this process at least once a year, sometimes more often if you have particularly dirty water or simply use a lot of RO/DI water. Just be sure that you monitor your filter cartridges' performance closely to ensure your getting the most out of your new filters while also not allowing contaminants into your aquarium. 

Changing your RO Membrane is a different process but should only need to be done every 2-3 years under normal use.  

READ ARTICLE: How To Change Your RO Membrane