Write-Up Wednesday: When I Actually Care About pH In A Saltwater Aquarium

Besides temperature, salinity, Ammonia (NH4), Nitrite (NO2) and Nitrate (NO3), pH is one of the first water parameters that you learn about in the water tank hobby. PH measures the concentration of hydrogen (H+) ions in solution. It is an easy level to test with test kits and even pH probes are inexpensive and can be quite accurate.

One of the first things you learn about pH is that 8.3 is “optimal”. You are then quickly bombarded with advice and additives to correct a pH level that isn’t exactly 8.3. Even seasoned saltwater tank hobbyists will chase a 8.3 pH level with often detrimental effects on their tank and wallet.

For mine and my client’s tanks, I pay very little attention to specific pH levels. PH is often monitored only because their aquarium controller came with a pH probe so I might as well set up the probe. When I do pay attention to pH is when I’m dosing kalkwasser either in an auto top off (ATO) container or through a kalk reactor. When I am dosing kalk, the specific pH levels still aren’t of much importance to me. I’m only concerned about the trend in pH, specifically the amount of change during top off events or when the kalk reactor runs. A pH change of .03 per top off or kalk dosing event is acceptable and I monitor this trend very carefully when using kalk.

Overall parameter trends in a saltwater tank mean a lot more to me than specific parameters levels. Every tank has parameter trends that make it happy and parameter trends that make it unhappy. Learning a tank’s personality, how parameter trends play into that personality and what to do once you learn your tank’s personality are some of the core components of my Chemistry and Tank Automation Program which is open now

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Comments for this article (6)

  • Tim Sendrowski says:

    Once again,
    another great article Mark.

  • jason says:


    What led you to the .03 PH change being the upper limit? is there literature or anecdotal evidence showing this is when issues start popping up?


  • Jason…I observed bleaching issue with SPS when I exceeded the .03 pH change when using kalk

  • Robert says:

    I’ve had no issues with a swing of 8.0 to 8.2+ using a calcium reactor supplemented with kalk.

  • Robert Scott says:

    I’ve had no issues with a 8.0 t0 8.2+ swing using a calcium reactor and kalk supplement. Heavy SPS

  • Damion says:

    In South FL where our house is closed up and our AC is on 11 1/2 months out of the year, I tend to have some CO2 issues in my home suppressing my tanks pH. I’ve learned to live with lower pH (7.9-8.1). Even when my dkh is around 9-9.5, but I do get a little antsy when it drops below 7.8, (and my corals don’t look so happy), so to curb this I use soda lime (CO2 scrubbing media) in a dry reactor on the air intake of my skimmer to get it up to the 7.9-8.1 I currently have.
    If you want to test this and see if you have a CO2 issue with your homes air quality, open your house up, and if your pH jumps up in a short time, then you may need some soda lime too.
    Some people use those home air exchangers, and some run a fresh air intake line from outside to there skimmer, but the soda lime option is best for me.
    Thanks Mark.

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