Holding a steady pH as close to 8.3 as possible has some significant benefits in a reef aquarium. Specifically for coral growth, health, and metabolic processes which is why reef tank owners shoot for this number. A vast majority of low pH problems are either because of low alkalinity or too much carbon dioxide in the air surrounding your tank.

By definition, pH is a scale of acidity from 0 to 14. Alkalinity is the capability of water to neutralize acid and carbon dioxide levels have a direct correlation with the amount of carbonic acid in the tank. So the better the ability to neutralize acid and the lower the carbon dioxide (carbonic acid), the higher the pH we can achieve.

Hanna Colorimeter Alkalinity Checker

Popular Alkalinity Test Kits

#5 - Maintain alkalinity properly

Alkalinity is the number one major element parameter to monitor and maintain in your reef tank. Alongside temperature, pH, and salinity, severe fluctuations in Alkalinity can cause a tank to crash. Specifically, your corals will stress out and perish causing a rise in nutrients and other toxins. pH will plummet or skyrocket too which can then negatively affect the fish and other animals.  

The commonly recommended target of 8.5 dKH is a safe range because it allows for dosing or testing mistakes without getting you into too much trouble. If your alkalinity goes up or down slightly from here, it will not have immediate detrimental effects.

BRS Sodium Bicarbonate

Simple sodium bicarbonate and water solution is the best way to raise alkalinity. Use our handy reef calculator to find the correct dosage for your tank using current and target Alkalinity levels. Avoid anything labeled “pH Buffer” because some products contain other elements that are not desirable in a reef tank or simply contain sodium bicarbonate in a fancy package at 10 times the price.

Don’t forget about calcium too! Alkalinity and calcium are both consumed at the same rate and you need to maintain both on a regular basis after achieving the target levels. For a majority of reef tank owners, this is done with your favorite two-part solution or all-in-one additives such as Tropic Marin Carbo Calcium or All For Reef. A calcium reactor and kalkwasser (calcium hydroxide) are also very popular maintenance options for reefers with a bit more experience.

Cloudy tank because of alkalinity additive

#4 - Use calcium and alkalinity supplements that are known to raise pH

These will be two-part solutions made from Soda Ash (sodium carbonate) as well as kalkwasser, both of which will reduce available carbonic acid and raise the pH. When shopping for a supplement to maintain alkalinity, simply choose one of these options. 

This is a good time to note the difference between raising alkalinity and maintaining it. We recommend unique solutions but there is some overlap here. When alkalinity falls out of range, you will adjust back into range using sodium bicarbonate because the tank can take a larger dose, without experiencing a drastic pH spike. Calcium, on the other hand, can be both adjusted and maintained using a calcium chloride solution since it doesn't have the pH spike associated with it.   

  • Sodium carbonate: Basic compound, caustic in nature and will create a pH spike when dosed into the aquarium. (Soda Ash)
  • Sodium bicarbonate: Basic compound, less caustic than sodium carbonate and you won't see a dramatic pH spike when dosed into the aquarium. (Baking Soda)

Once you reach that target level, alkalinity and calcium are then maintained daily with sodium carbonate, kalkwasser, two-part solutions, calcium reactors, and sometimes a combo of these things. The daily dose designed to only replenish what your corals consume every day is much smaller compared to an adjustment dose, and therefore, the smaller more incremental pH boost is desirable.

The process is simple, adjust alkalinity to the desired range with a sodium bicarbonate dose first, then maintain daily moving forward with sodium carbonate. Should you notice the alkalinity drops over time, adjust again and increase your daily dosage enough to maintain rock-solid alkalinity levels on a daily basis. The same concept is applied to calcium but you don't have to switch up the solution.

Learn More With BRStv: Find Out Which Alkalinity Supplements Have The Biggest Impact On pH

Open Window

#3 - Reduce carbon dioxide levels around the tank

This is the direct result of tightly sealed homes or rooms with lots of pets and people who breathe out carbon dioxide all day long. This elevated level of CO2 will increase the pH in your tank because of the natural gas exchange that occurs. The easiest option is just to open a window for a few hours each day to let fresh air into the house. If the pH of the tank goes up, then too much carbon dioxide in the air around your tank is suppressing your pH.

It isn’t really viable to keep the windows open during the coldest or hottest months of the year so the implementation of special equipment like air exchangers are the best option

Protein Skimmer

CO2 Scubbers
  1. CO2 Scrubber Skimmer Lid
    Reef Octopus
    CO2 Scrubber Skimmer Lid
    From: $29.99

  2. AF Air Scrubber Hose
    AF Air Scrubber Hose

  3. AF Air Scrubber Media
    AF Air Scrubber Media

  4. AF Air Scrubber
    AF Air Scrubber


#2 - Pull fresh air from outside or CO2 scrub the air entering your skimmer

Your protein skimmer creates a tremendous amount of gas exchange, far more than what happens at the surface of your tank interacting with ambient air. So if CO2 is your issue, running a tube through the wall to pull fresh air from outdoors into your protein skimmer will very often alleviate the suppressed pH of the tank.

Just make sure not to draw from a heavily polluted area where pesticides and fertilizers are used. Adding some carbon on the intake side can help remove such pollutants or contaminants and is an excellent safety precaution.

CO2 Scrubber

Alternatively, it is becoming quite popular these days to remove all the CO2 using a scrubber. Using special CO2 absorbing media inside a sealed canister such as the BRS reactor, attached to the air intake will remove CO2 before it enters your skimmer.

Protein Skimmer Air Intake with WYE Fitting

This method is very effective in terms of elevating pH, sometimes a bit too effective. If you are running a strong skimmer for your tank size and substantial flow through rates, it may need to be throttled back using a wye fitting or else the pH will get too high!

Electronic Solenoid

For all you control freaks and die-hard reef nerds like us, you can automate this process using an electronic solenoid attached to the CO2 scrubber WYE fitting. Just peg the pH in your controller and tell it to open and close the valve as necessary to maintain that golden pH number of 8.3. When pH is too low, the valve will be closed forcing air to be pulled through the scrubber, when pH is too high, the valve will be open and pulling ambient air.


#1 - Grow a refugium with macroalgae

A proper refugium growing macroalgae like chaetomorpha will rapidly consume excess carbon dioxide from the water, reducing carbonic acid and raising the pH level.

We like this method the best for a few reasons. It is natural, does not require that you purchase media on a regular basis, it works for anyone willing to put forth the effort, and you can tune the growth rates by adjusting light intensity and photoperiod.

Kessil Refugium Light

A refugium also provides the additional benefits of removing nitrates and phosphates and competes with nuisance algae in your display. In fact, one of our most popular BRStv Investigates experiments was when we ran some prolonged experiments on various refugium light sources to research the effect on nutrient removal and nuisance algae growth.