Boardroom Aquatics, Inc.
Home      pH & Alkalinity


Natural seawater in shallow reef zones has an average pH of 8.4. With this in mind, the normal recommended pH for a reef tank is 7.9 - 8.4. Keeping a balanced pH can be difficult. It is imperative that the marine aquarist understand the roles Carbonate Hardness / Alkalinity, oxygen / CO2 levels and water quality play in helping to maintain a specific pH.

Simply put, pH is the measurement of a liquids acidity level. The pH scale runs from 0 to to 14 where a pH of 7.0 is considered neutral meaning its neither acidic or basic. A pH level greater than 7.0 is considered basic while less than 7.0 is considered acidic. Lower pH substances would include battery acid while higher pH substances include items such as bleach and drain cleaner. The pH scale is logarithmic based, meaning that each whole number increase or decrease is a tenfold difference. A liquid that changes pH from 8.2 to 7.2 became ten times more acidic. Keep this scale in mind when trying to modify the pH of your aquarium, pH adjustments should be done gradually over time.

Alkalinity is the measurement of a substance resistance to change in pH. The higher the resistance the higher the alkalinity. Substances that help to minimize change in pH by raising the alkalinity level are normally called buffers.  Some of the most widely used buffers in the marine hobby include carbonate and bicarbonate.  By properly maintaining your alkalinity level you go a long ways towards maintaining a stable pH level.

Alkalinity can be measured in a number of ways. One of the easiest and least expensive methods is by measuring the carbonate hardness of your tank water. The measurement is in degrees of carbonate hardness or dKH. It is recommended that you maintain carbonate hardness between 8 and 10 dKH. 

Note: The pH of your tanks changes slightly throughout the day and night. As a aquarist it is our desire to minimize these swings in pH. To that end it must be noted that the oxygen / CO2 levels in your water will certainly affect your pH level. During the day algae undertake a process called photosynthesis whereby they convert light energy and CO2 to oxygen. This reduction of CO2 will keep the pH higher during daylight hours. You lose this natural process when the lights are off.  Therefore the more algae you have in your tank the larger a swing you will have between lights on and lights off pH. For this reason many hobbyists keep a refugium stocked with macroalgae and run the refugiums light schedule opposite of the main tank thereby keeping the photosynthesis process going 24 hours a day.  

Getting back to water quality, decaying food, nitric acids and phosphate all tend to push your pH level down. As these items build up you will most certainly see a slow drop in your pH. This process can be slowed and or halted by consistent water changes and properly maintaining the buffering capacity of your water. High particulate matter, older water and low alkalinity could be a recipe for disaster.

Test your pH on a normal schedule. Monitor your pH levels, work diligently to maintain a proper alkalinity level and strive to keep your water quality as high as possible . Do all this and you are well on your way to succeeding as a marine aquarist! 

Boardroom Aquatics  |  Aquarium Sales   |  Service  | Rare Tropicals 
Fort Myers, Florida
Our website and security policy may be found here. Click to review these policies.