How to raise pH in saltwater tank with a CO2 scrubber - BRStv Reef FAQs

For those of you looking for the growth and metabolic health benefits of maintaining a pH of 8.3, scrubbing CO2 is one of the easiest and most reliable ways to achieve that goal.

Presuming you are maintaining alkalinity properly, high carbon dioxide (CO2) in the air surrounding your tank is the #1 cause of low pH. Excess CO2 in the air transfers to the tank via natural gas exchange and creates carbonic acid which lowers the pH of the tank.

An air exchanger on your AC or furnace is the best solution but it is expensive if you don’t already have one. Opening a window and/or doors for 24 hours will let the excess CO2 escape also and should be your first step in order to identify that CO2 is indeed your problem.

If pH rises after opening the windows for 24 hours, then you can be fairly confident that excess CO2 is suppressing the pH in your aquarium.

How to use a CO2 Scrubber

Since keeping windows and doors open year around is not really possible for most of us, using a CO2 scrubber is an excellent solution that will work on any tank with a protein skimmer.

The scrubber attaches to your protein skimmer air intake and contains CO2 absorbing media that will remove a vast majority of CO2 gas from the air before it enters your skimmer. This prevents the formation of excess carbonic acid and effectively raises the pH.

The reason this works so well is because modern skimmers create a huge amount of gas exchange that exceeds what naturally occurs at the surface of your tank.

As the CO2 media gets depleted it changes color and how long the media lasts is dependent on how much CO2 is being scrubbed.

Here at BRS we have created a couple of handy kits with different size media cartridges to suit your needs. The smallest Universal CO2 scrubber includes the standard 10” cartridge, followed by a larger Jumbo Single Canister unit with x4 the capacity and then a Dual Jumbo unit with x8 media capacity.

All of the kits come with 3/8” barbed fittings and tubing to easily attach your skimmer airline. If you need adaptors, we suggest the Kynar ozone fittings. There are a range of sizes and options including tees, wyes, and couplers that will accommodate the smaller diameter tubing on protein skimmers.

The BRS CO2 scrubber kits also include a wall mount bracket or leg stand option to accommodate various mounting situations.

In most situations, operation is as simple as connecting the reactor and watching your pH climb into a more ideal range. In some cases, however, it works too well and will raise the pH more than what you might like.

To control the amount of CO2 being removed, you have two options. It can be done manually by adding a wye fitting and valve on the fresh air side of the wye. Valve back the fresh air in small increments until the desired pH is maintained.

For the more technologically inclined, you can also use the wye fitting but attach an electric solenoid on the fresh air side instead of a valve. Many will just connect the solenoid to a timer so the air is only scrubbed at night when the pH is the lowest.

If you have a pH controller or aquarium controller like the Neptune Systems Apex, you can automatically open and close the solenoid based on pH measurements in your tank to create ultra stable pH, 24 hours a day.

When pH is too low, the controller will close the valve forcing all of the air to pass through the scrubber and increase the pH. When pH climbs too high, the valve will open allowing fresh air to enter the skimmer and keep the pH within range.

One solenoid is sufficient but you could of course add two, one on each side of the wye for more precision control. We have used the ?” push-connect solenoid from McMaster-Carr in the past.

Is a CO2 scrubber right for you?

If elevated CO2 levels in your home is not the issue, than a CO2 scrubber will not work to increase pH in your aquarium. That is why it is important to perform the open window test first.

Another situation in which a CO2 scrubber may not work is if your running a really large aquarium with a grossly underrated skimmer. Something like a 200 gallon display aquarium with an old skimmer with an exaggerated rating for 75 gallons. This is because the natural gas exchange happening at the tanks surfaces will overcome what is happening inside the small skimmer.

Maximize the media

A single cartridge (1.2 lbs) of CO2 absorbing media is about $6 and the larger single cartridge refill costs about $24.

Nobody likes the idea of adding yet another consumable media but considering what we learned in a recent BRStv Investigates about elevated pH and coral growth, it is well worth the expense. Especially when growing frags and establishing a young reef tank with new corals.

We measured up to 30% faster coral growth over a 3 month period when pH was maintained consistently at 8.3.

With this in mind, there are ways to extend the life of the media and increase your return on investment. Using the wye fitting and valve we described above is the most effective, especially if your running a powerhouse protein skimmer that draws substantial amounts of air.

By throttling the fresh air being pulled through the scrubber you can also choose to maintain your pH at 8.1 instead of 8.3 which will result in less media consumption. In fact, this minor pH change of only 0.2 could result in as much as 50% less media consumption. Think of it like tuning the scrubber to meet the needs of YOUR tank and budget.

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