KH Spike, PH Drop!

My KH has been running in the low 8s for quite a while and I decided to buffer it to get it into the 9.5 range. I picked up some IO Sea Buffer and dosed it at 2/3 the recommended amount. The KH went to 11.8 and my PH remained at 8.2m where it has always been

The instructions said to dose daily until desired level was reached so, obviously, I didn't re-dose. It dropped throughout the week, slowly (checked it daily) and when it reached 9.5, I dosed again with 1/5 the recommended amount. 2 days later, it was up to 15.7 and my PH was down to 8.0. I retested with the same reading. Thinking it was the kit, I tested some mix water and it was spot on at 9.6. Took some to the local saltwater lfs and the reading was correct

Several water changes and 5 days later and the alkalinty is still dropping and is into the 11s but my PH is hung at 8.0.

My question is why did this happen and why didn't my PH go through the roof as well? My second test was PH and I remember thinking "Don't be 9, don't be 9"(my wish came true, unfortunately) as I expected the PH to follow suit with the KH

Is there any way to raise the PH safely, without raising the alkalinity? Most of the methods I know raise the PH through raised KH.
If you does vodka and/or vinegar. you may have problems with alk and ph.

I don't dose anything. All my params are dead on; 0 NOs, 0 PO4,CA always between 460 and 480 (still, with the KH spike: another mystery), everything but my alkalinity staying at 8.5 and below, which I'll GLADLY learn to accept when this is all over

Nothing that should have happened when KH goes up, did. My ph should have risen with it, it dropped. My CA should have dropped, it didn't. This one is beyond my experience...and I'm done dosing over trivial parameter variances from "optimal"


-RT * ln(k)
I wouldn't worry with the pH. Just let the alk drop down or maybe do a water change to help.
Definite on the water changes. I've swapped out 30% since it happened Weds. Did 2 15s as I was worried about what dropping it too fast might do
Is there any way to raise the PH safely, without raising the alkalinity? Most of the methods I know raise the PH through raised KH.

As long as your pH remains between 7.8-8.5 you are fine, like stated. ;)

Opening windows to let fresh air in the house will allow your pH to increase since the reason for your low pH is high levels of CO2 in your home from breathing. This extra CO2 in home air will enter the tank water and decrease pH. Gas and oil appliances that are not properly vented like ventless gas fireplaces will increase house CO2 levels as well. :)


ReefKeeping Mag staff
Premium Member
The amount of CO2 in the water is the cause of CO2 variatons. Using alk buffers to manage it seems to work short term but leaves higher alk and virtually the same ph over a relatively short time, as CO2 equilibrates between the air and the water.Bounces in alk levels are harmful to corals . Ph in a range of 7.8 to 8.5/6 dkh is not.

The CO2 comes from the house air and from activity in the tank( bacterial activity and respiration by photosynthetic organisms at night as examples).If the house air is high in CO2 and gas exchange to the tank water via surface agitation and open water is good ,the CO2 in the tank will move up to the level of the house air and the ph will go down. Fresh air via open windows or an airline to the skimmer intake should help in this case.
Testing a sample of tank water aerated for a few minutes inside and then aerated and tested again outside can determine the house CO2 level relative to the outside air .
If the house air is normal in CO2 content then increased gas exchange via open water and increased surface agitation should help move CO2 from other activity out of the tank more quickly, thus increasing the ph.
Another method for reducing CO2 input is a CO2 scrubber which can be attached to the skimmer air intake line.
Dripping kalk will reduce CO2 as it uses it to make carbonate/bicarbonate alkalinity. So it increases alk but if used in lieu of buffers and calcium supplements at the right level it can be used with no increase net effect on alk.


Premium Member
I agree that carbon dioxide is the main driver of pH in our tanks, assuming the alkalinity is reasonable. There's no additive that can increase the pH without also increasing the alkalinity, pretty much by definition. An alkalinity supplement can add carbonate alkalinity and reduce the pH by adding carbon dioxide at the same time, the way baking soda does.

I would dose buffers based only on the alkalinity level, as has been suggested.