What exactly is PH?
PH is the measure of relative concentration of hydroge ions and Hydroxyl Ions in your aquariums water.
This measurement indicates if the water is acidic or alkaline.  A PH of 7 is considered neutral, If the PH is below 7 its acidic and above 7 its alkaline.


PH levels in your aquarium are very closely related to the CO2 and alkalinity levels in your aquarium. As CO2 enters the water it will turn the water acidic and lower the PH (this is essentially how a calcium reactor works)

Assuming the CO2 is in the tank at equilibrium with the outside air then the Alkalinity level would determine your PH

Why is the PH higher when the are on?
When your lights are on the organisms in your tank are preforming photosynthesis and converting co2 into oxygen..   At night the lights are off and and photosynthesis is no long occuring..
What ph should reef tank be

A generally accepted range for PH in a reef tank is: 7.6-8.4  However the ideal PH would be 8.0-8.3
That being said many have highly successful reef tanks with a PH less than 8.
What causes low PH in a saltwater aquarium?
-Excess CO2 in your home is the most common cause.
– people and pets breathing in the house
– CO2 reactors
-Carbon dosing


My PH is low.. How can i raise it?
– Open a window to allow fresh air into your home
– Increase surface agitation by pointing power-heads towards the surface to promote gas exchange
– Run an air intake line for your skimmer or airpump outside to draw in fresh air
– Raising your Alkalinity level can also raise your PH
– Dripping Kalkwasser into your tank or adding it to your ATO (2 tsp/gallon)
– Install a small PC fan into your cannopy to allow fresh air into the tank
– Leave part of your sumps cabinet open to allow more gas excahnge
– Use a wooden air-stone at night (Micro bubble scrubbing) which I run at night.
– Co2 scrubbing media on your Skimmer intake
– Run a refugium on a reverse light cycle
– Run an Algae Turf Scrubber
– If your using a CO2 Reactor – try adding a second chamber or add a drip cup to let the effluent off gas.

** Note: Injecting air form an air pump or wooden airstone will only raise the PH if the air your injecting has a lower CO2 concentration than your tank. If your room has a high co2 concentration you may want to suck air from out side.

*Do NOT use a PH buffer as it will just cause swings and potential issues for your take organisms


As a word of caution.. PH can be one of those rabbit holes so if you try a few of the above suggestions and your still having issue but your corals look happy..dont worry about it!

If your a reef geek and want to dive deeper into the science behind PH, check out this article by Randy Holmes