CDX 750 ml and 3 L — CO₂ Absorbing Media for Protein Skimmers - Two Little Fishies

A pH that refuses to climb no matter what you dose? In a sealed house, CO2 builds up in the air — and as long as that air feeds your skimmer, your tank's pH won't hold. Two Little Fishies' CDX goes after the cause: it's a carbon dioxide adsorption media ("adsorption" is the manufacturer's exact word) that scrubs the air before it enters the skimmer. Two sizes: 750 ml jar (25.4 fl oz) and 3 L bucket (0.8 US gal).

How it works

The manufacturer's principle fits in one sentence: once the skimmer is fed CO2-free air, that air draws the excess dissolved CO2 back out of the water, and the pH rises. You stop fighting the symptom with buffers — you pull the cause out at the source.

Installation

The official instructions: load the CDX into a PhosBan reactor, then connect the reactor to the skimmer's air intake with a length of hose and the CDX adaptor. That's exactly the setup shown in the product photo. We carry both reactors: the PhosBan 150 for the 750 ml jar, and the PhosBan 550 when you're working from the 3 L bucket. The CDX adaptor isn't in our catalog yet — email us before ordering and we'll sort it out for you.

Specifications

• CO2 adsorption media for the skimmer's air intake
• Targets pH instability caused by CO2 accumulating in closed buildings
• Runs in a PhosBan reactor, connected to the skimmer with a hose and the CDX adaptor
• Official sizes: 750 ml jar (25.4 fl oz) and 3 L bucket (0.8 US gal)
• Precaution: wear gloves when handling the product

Two Little Fishies does not publish how long a charge lasts. If you see a number somewhere else, it didn't come from the manufacturer — it depends on your indoor CO2 level and your skimmer's air draw. Email us and we'll help you size it.

Available sizes

• 750 ml (25.4 fl oz) — UPC 748172402313
• 3 L (0.8 US gal) — UPC 748172402320

Why buy from ReefSolution

In business since 1999, with over 118,000 orders processed since 2010. In-store advice in Laval, QC, shipping anywhere in Canada.

The follow-up companion: chronic low pH should be documented before it gets treated — the Salifert KH/Alkalinity test kit tells you whether the problem is airborne CO2 or a sagging alkalinity.

Our advice

CDX is aimed squarely at people with a chronic low-pH problem — the ones who can never get their pH up. Very often it comes down to a house that doesn't breathe enough: there's too much CO2 in your indoor air. Since you can't open the windows in winter, or in summer with the air conditioning running, you hook up the CDX — in a reactor or a container — and the air passes through the CDX before the skimmer draws it in. It strips out the CO2, and your pH climbs instantly.

— Stéphane, Aquarium ReefSolution

Frequently asked questions

Why does my reef tank's pH stay low?

Very often because your indoor air is loaded with CO2 — windows shut all winter, air conditioning all summer. The skimmer draws in that air and dissolves it into the water. Scrubbing the intake air with a media like CDX raises pH without touching your water chemistry.

How do you hook up CDX to a skimmer?

Per the manufacturer: the media goes in a PhosBan reactor, and a hose connects the reactor to the skimmer's air intake through the CDX adaptor.

How long does a charge of CDX last?

Two Little Fishies doesn't publish a duration. It varies with your ambient CO2 and your skimmer's air draw — email us with your setup and we'll help you estimate it.

750 ml or 3 L — which one should I get?

Same media in both containers. The 3 L works out cheaper per litre and gives you several reactor refills; the 750 ml is the ideal starter size.