6 Steps to Stable pH in a Saltwater System

Like other water parameters in your marine aquarium, stability is also important with pH

Like other water parameters in your marine aquarium, stability is also important with pH

Stability of water parameters is essential to success with marine aquariums, especially when it comes to keeping sensitive invertebrates. Among the various parameters that hobbyists often struggle to maintain at an appropriate level is pH, essentially a measure of how acidic/basic the water is.

While the ideal target for pH in a marine aquarium is somewhere in the range of 8.2 to 8.4, it’s more important to maintain a stable pH, even if it’s slightly outside this range, than to constantly chase a particular value within the range. The challenge is, owing to various natural processes going on in the tank, the pH in a closed aquarium system usually drifts downward (there are exceptions, of course), so the hobbyist must take certain steps to counteract this trend. Here are six of them:

1) Perform regular partial water changes

Regular Saltwater Smarts visitors must be pretty tired of hearing this by now—as I recommend water changes for virtually anything that ails a saltwater system. But the truth is, nothing promotes stability of parameters, pH included, better than routine partial water changes. Every time you replace old salt water with new, you’re not only removing dissolved pollutants and replacing components vital to the health and growth of your livestock, but you’re also replacing compounds that buffer the water against shifting pH (carbonates and bicarbonates).

2) Aerate and agitate

Providing good, robust water flow throughout the system along with surface agitation will help increase oxygenation while driving off pH-lowering carbon dioxide. Strategically positioned submersible pumps and sump returns along with the use of a good protein skimmer will be your allies here.

Also keep in mind that if the room containing the aquarium is confined, poorly ventilated, and/or heavily trafficked, the carbon dioxide concentration in the room may be higher than normal and, thus, you may have ongoing problems with low pH in the aquarium. Increasing ventilation (e.g., by opening a window if possible) can help mitigate this.

3) Stock and feed judiciously

The more animals you have in a tank, feeding, respiring, and producing waste, the more likely it is that your pH will drop over time. I’ve always stocked my aquariums very lightly and have had very few issues with pH over the years. Also, when it comes to fish, I prefer to offer small, frequent feedings, in which most of the food is gobbled up quickly, rather than less frequent, heavier feedings that allow bits and pieces of uneaten food to drift into nooks and crannies where they can decompose and degrade water quality.

4) Supplement calcium/alkalinity in a balanced manner

In many reef systems, especially those housing stony corals and/or clams, calcium and alkalinity must be supplemented to keep them at proper levels. However, haphazard dosing of these elements can have an adverse effect on your pH. Because water can hold only so much in the way of dissolved solids, adding more of one element tends to drive down the other. So, for example, if you notice that your calcium level is lower than desired and you try to remedy it by supplementing calcium alone, your alkalinity level may decline, leaving the system more vulnerable to a subsequent drop in pH.

Calcium and alkalinity should be supplemented simultaneously, using a method such as a balanced two-part supplement, kalkwasser, a calcium reactor, or some combination of these techniques (e.g., folks who employ a calcium reactor, which produces a relatively low-pH effluent, will sometimes also drip kalkwasser, which has a very high pH).

5) Take a “trust but verify” approach to pH test results

Obviously, regular testing of your pH level is essential if you hope to detect any unusual deviation and correct it before it becomes a major problem. However, in some cases, a system’s pH level is just fine, though the hobbyist’s test kit/electronic meter might tell a different story.

Before taking off-kilter pH test results at face value and implementing measures to correct them, ask yourself whether you’re truly confident in your testing method. Test kits should be relatively fresh (i.e., the reagents haven’t expired), trusted for both accuracy and precision, and used properly in accordance with the manufacturer’s directions. If you use an electronic pH meter, it too should be a high-quality brand/model of proven reliability and must be properly cleaned and calibrated.

6) Test your pH at the same time of day

To make sure you’re comparing apples to apples, so to speak, it’s helpful to test your pH at the same time of day. The reason being, due to the natural processes of photosynthesis and respiration, a system’s pH will tend to rise gradually throughout the day and then fall gradually throughout the night. This isn’t typically a major swing, but it’s notable nonetheless. So, if you test your water at the end of the day one time and then first thing in the morning the next time, you may get an incorrect sense of the overall trend.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Paul Baldassano says

    I took your advice and opened a window to stabilize the pH in my tank. It may now be stable but being the tank is a solid block of ice, I can’t test it.

    • Jeff Kurtz says

      Ahh! In that circumstance, you’ll need an “extremely low temperature” pH test kit–and an ice auger.

  2. Thank you for the pH control guide. It’s invaluable as ever.

  3. Loved the pH quide. I, too, am an avid SCUBA Diver and love marine fish. It has been a challenge to set up a true marine like reef tank and appreciate the advice.

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