Two Little Fishies CDX Carbon Dioxide Adsorption Media

Two Little Fishies CDX is a carbon dioxide (CO₂) adsorption media designed to help raise and stabilize pH in saltwater reef aquariums by removing CO₂ from the air before it enters your protein skimmer.  

Key Features

• Removes CO₂ from the air supplied to your protein skimmer.
• Helps increase and stabilize aquarium pH naturally.
• Ideal for reef tanks in homes with elevated indoor CO₂.
• Works in a PhosBan Reactor or similar media reactor connected to a protein skimmer.
• Color-changing media indicates when replacement is needed (white to pink/violet, depending on the batch).  

How to Use

• Fill a media reactor with CDX.
• Connect the reactor outlet to your protein skimmer’s air intake using the appropriate tubing and adapter.
• Replace the media when it changes color, typically every 6–8 weeks on a 50–100 gallon reef aquarium, depending on indoor CO₂ levels.  

This product is especially beneficial if your reef tank consistently has a low pH (around 7.7–8.0) despite having proper alkalinity, as excess indoor CO₂ is often the cause.  

All livestock ships via FedEx Priority Overnight, double-bagged and temperature-protected with a heat or ice pack as needed for your destination.

Florida orders under $299 ship for $25; out-of-state orders under $299 ship for $40. Orders over $299 ship free. We don't currently ship to Alaska, Hawaii, Puerto Rico, or outside the continental U.S.

Free in-store pickup is always available — contact us for details.

If your coral arrives dead on arrival (DOA), report it within 2 hours of the delivery time shown on your FedEx tracking — email a clear photo to info@strictlyfishmiami.com and we'll issue a store credit for the purchase price of the livestock.

See our full Refund Policy for details.