pH and Alkalinity

ph and alkalinityHow pH and alkalinity are related, and why it is critical to maintain both at ideal levels in our saltwater aquarium.

What Is pH?

pH stands for ‘power of Hydrogen’, and is a measure of how acidic or alkaline a liquid is. pH ranges from zero to 14, with 7.0 being neutral.

The pH of natural seawater is around 8.0 to 8.3.

In our saltwater aquariums, a pH ranging from 8.0 to 8.4 is fine, with stability being the key. Wide swings in pH in too short a time can cause osmotic shock in our fish and corals.

What Is The Cause Of Low pH?

Acidity, or chronically low pH is caused by pollution from fish waste, overfeeding, overstocking and the resulting metabolic impact all these have on our aquarium. Poor aeration and a lack of water changes can also result in depressed pH.

If all of these factors are addressed, pH can be returned to desirable reef levels and remain consistent.

Later, we will discuss the relationship between pH and alkalinity and how a drop in alkalinity will also lower pH.

Why pH Levels Drop At Night

Algae and other organisms consume carbon dioxide during the day and release carbon dioxide at night. This excess carbon dioxide causes pH to drop. Depending on our stocking levels and the amount of algae we have in our aquarium, the drop in pH can be anywhere from 0.1 to 0.5. Buffering up our daytime pH to 8.3 or 8.4 will ensure that it doesn’t reach overly low levels at night.

How To Increase pH In A Saltwater Aquarium

pH can be raised by dosing commercial additives. Seachem’s Reef Buffer is good for raising pH and is dosed according to the water volume of the aquarium.  Since pH and alkalnity are closely related, as we will soon discuss, we should bear in mind that most pH buffers will also raise alkalinity.

pH in a saltwater aquarium should be increased very slowly, preferably not more than a 0.1 increase over a 24 hour period.

What Is Alkalinity?

Alkalinity is water’s ability to resist changes in pH.

In our aquariums, our tank inhabitants continually produce acids that will drive down pH. Alkalinity, in the form of carbonates, ensures that pH remains steady in spite of the continual production of acids by our tank inhabitants.

In our saltwater aquariums, our alkalinity’s buffering capacity is measured in dKH or carbonate hardness. A healthy range is anywhere from 7 dKH (natural ocean levels) at the minimum, to 12 dKH maximum.  An ideal level of 9dKH would give some leeway should alkalinity drop.

How pH And Alkalinity Are Related

Carbonates are constantly being absorbed by many life forms in our aquarium.  Over time, these carbonates, which also form the alkalinity buffer of our water, get depleted.  This drop in alkalinity leads to increased acidity in the water, causing pH to decline.  This is the critical relationship between pH and alkalinity.

How To Raise Alkalinity In A Saltwater Aquarium

Other than maintaining pH, carbonates themselves are also important to coral skeletal growth and this is another reason we would want to maintain good dKH levels in our reef aquariums. This can be achieved with a good additive like Seachem’s Reef Builder, which as a bonus will also raise magnesium.

My pH Is Too High.  What Do I Do?

There are some rare instance when the pH in a saltwater aquarium exceeds 8.5, bringing pH out of the desirable range.  Overly high pH can lead to precipitation of calcium carbonate, depressing calcium and alkalinity in the process.

Surprisingly, high pH is often caused by a lack of carbon dioxide in the aquarium water!

High pH is best addressed by 15% water changes performed daily over 2 or 3 days or until pH is normalized.

It is also possible to increase the acidity in the aquarium water by means of vinegar (acetic acid) or with soda water with its bubbles of carbon dioxide.  These two methods of reducing pH require due dilligence and care so as not to drive the pH down too low.


Links to more pages on Water Parameters:

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