How to Raise pH in a Saltwater Aquarium Safely

Saltwater tanks require a higher emphasis on pH than the majority of freshwater systems. Without it, your fish and corals are at the mercy of dangerous fluctuations that can cut their lifespan short. It’s not too hard to raise and maintain a high pH if you know what you’re doing.

So, let’s get into it with what you need and how to raise pH in a saltwater aquarium safely.

ph balance


What You Need

You’ll need a few things, especially since we’re going to take a multi-prong approach to make sure that pH stays within an acceptable range for your creatures.

Get your hands on the following:

  • Baking Soda- Any brand will do as long as there are no additives. We just need some 100% sodium bicarbonate. Arm & Hammer works just as well as the mixtures sold specifically for saltwater aquaria, at a much lower cost. 
  • Refugium- Containing macroalgae that eat CO₂, a refugium is a great idea to help stabilize your tank’s pH. You can also purchase enclosed macroalgae reactors but they’re rather expensive.
  • CO₂ Scrubber These are attached to your protein skimmer and remove dissolved CO₂ from the water, thus raising the pH.
  • pH Monitor A pH monitor isn’t required, but it will make your life a lot easier. You need to see what your daily fluctuations are.

The astute reader will note that only one of those items directly affects the pH of the tank. Baking soda is used to get our pH where we want it, everything else is how we keep it there.

One overlooked bit of tank chemistry for new marine keepers is the effect of carbonic acid on the pH of our water. CO₂ is exchanged at the top of the tank’s water, and levels naturally go up at night when photosynthesis is no longer taking place.

Your pH will naturally fluctuate because of this. Your pH monitor will help you determine how much of your pH problems are coming from this cycle.

You also need to understand the difference between alkalinity and pH. While the two terms are sometimes used interchangeably, they actually measure different things.

pH is a measure of the free hydrogen ions (H+) that are in the water. Alkalinity, on the other hand, measures carbonate and bicarbonate levels in the water. That’s why we’re using baking soda as our primary reaction to change the pH of the water.

High alkalinity levels will nudge pH higher, and also help to resist changes in the water. That includes both external sources and those that naturally occur inside the tank.

Putting all of this together gives us a short-term solution to our pH problem, which we can follow up with measures that will help ensure the pH remains stable over a longer period of time.

One more thing before we begin: if you’re using RO or distilled water to fill your saltwater aquarium then you should check the pH before you add it to the tank. 

Your salt and other chemicals should get the pH and dKH in a good spot, but if the problem starts at the source then you already have your solution.

1. Use Baking Soda to Lower the pH

Don’t just pour baking soda into the tank. It’s ineffective and inaccurate, and it can cause harm to your fauna.

Instead, pull about a cup of water at a time and place the baking soda in there. Add roughly a tablespoon at a time for tanks 30 gallons or larger, perhaps half of that for a smaller tank. Add the water back into the tank, preferably right next to a filter outlet.

If you’re using a HOB, you can actually just dump it at the top of the filter for faster distribution throughout the water column.

Give the water 2-3 minutes to circulate and then test the pH. It should raise a bit with each dose of the baking soda. Aim for your ideal pH or 8.0 if you’re not sure what the ideal is for your tank.

Once you’ve reached your pH, it’s time to take measures to keep it there. If you have a way to test alkalinity, in addition to pH, you should be aiming for 8-12 dKH. This is ideal for most reef tanks and provides a good buffer.

Please note that you shouldn’t move the pH too much at once. Try aiming for moving the pH only .2 or .3 per session for the best results. It may seem a small thing, but fish can die with less than a 1.0 change if it’s done too quickly.

Try to dose at the same time every day so that the pH you’re altering remains consistent with the photosynthetic cycle of the tank. 

2. Add a Refugium

Putting together a refugium isn’t hard, or you can purchase an enclosed one that’s commercially available.

A refugium is a simple concept: you grow algae in a separate container with the water being pumped from the tank into the refugium and out of it with another pump. Add light and your algae and you’ll be good to go.

A refugium can be used to stabilize the pH of the water by absorbing CO₂. Since plants (like your macroalgae) only take in carbon dioxide during their light cycle we have to time the lighting.

Usually, you’ll also have live rock and/or sand in there to help with bacteria and further raise the pH of the tank.


Time your refugium’s lights to run opposite the main tank’s lights. This will ensure there is a constant uptake of CO₂ from the water column, reducing the effects of lighting on pH fluctuation.

A refugium may be all you need. But you need to make sure that you don’t have to take other measures. Constructing a refugium in detail is a bit beyond the scope of this article, but there are endless guides to it available

Monitor your pH levels for the swing. pH should be highest at the midpoint of your lighting cycle. 6 hours in on a 12-hour cycle, for instance. It will be at its lowest just before the light is turned on in the morning.

A swing of .1-.5 is normal, but you want to be on the lower end of that range. If you’re not yet only swinging .1-.3 after installing a refugium you may need to take further measures.

3. Install a CO₂ Scrubber for Your Protein Skimmer

If you haven’t checked the alkalinity of your water yet and you’re still having pH swings out of your desired range then it may be the problem. This is relatively rare when you’re using sodium bicarbonate. After all, bicarbonate is a main component of alkalinity, but it does happen.

In this case, you need another tool to help manage CO₂ in your tank.

They’re a pretty simple device. You take the air outlet from your protein skimmer and hook it up to the scrubber after you put it in place. The container is then filled with a carbon dioxide absorbent which helps clean carbon dioxide from the air.

CO₂ scrubbers aren’t a common accessory. 

Simply put: a refugium and ensuring you have the right level of alkalinity (8-12 dKH) will usually handle the problem. A CO₂ scrubber should handle the rest.

Give things a few days after adding the CO₂ scrubber to see if they settle. If they don’t then you have a serious problem with atmospheric CO₂ or an interior tank problem, and you’ll need to move to the next step.

4. Check Your Environment for Problems

I don’t advise continuing to add equipment or chemicals to the water at this point.

The first thing to do is go over what’s in the tank. It’s pretty rare that the problem is internal, but it doesn’t hurt to make sure. 

The only “common” item that will mess with your pH in a saltwater tank is driftwood. I’ve seen people try to use it in marine tanks a few times and it will lower your pH. Adding strange stones is never a good idea either and they could potentially lower pH. That said, most are neutral or raise pH, and the main danger of pretty rocks is metallic ions dissolving into the water column.

Nothing strange in your tank?

Then you’re looking at a problem with the actual CO₂ levels in your home. This is most common in energy-efficient homes, where trapped air may not get enough circulation to bring in fresh oxygen from outside. 

So, it turns out shoddy window and door seals are actually good for one thing.

It can also be a problem if you’re living in a small space with too many people and pets.

Opening windows helps, as does making sure that all of your central HVAC filters are good and that your fans are running. You need some intake from outdoors with your central air.

If it’s just a room that hasn’t received proper ventilation in a while then you can probably open a window for a few hours to let the carbon dioxide out and some fresh air in.

The bottom line is this: if your pH isn’t holding despite proper alkalinity and the use of a refugium and CO₂ scrubber then you probably have a problem with the air quality in your home.

Any serious measures for mitigation of carbon dioxide in the home are beyond my expertise, and consulting a professional is a good idea. 

Carbon dioxide poisoning, with high levels over long periods, can cause illness and the issue should be addressed. That said, it’s still a rarity and you’re unlikely to have to go to these measures to keep your tank’s pH balanced.

One, Two, Three to 8.0

The bottom line is that raising the pH in a saltwater aquarium safely is often a simple matter. It just may take some time to sort out the issue as you add baking soda and then equipment. Learning how to do this safely is key, but it’s mostly just a matter of waiting a bit.

The real question here is what are you planning to keep now that you have a stable pH?