Aquarium Chemistry

pH

The pH value in aquatics, which is a measure of the acidity of the water, is a major “water value.” Organisms have a wide tolerance range for the different pH and can not be outside of this to survive. Determining whether a species found in an aquarium has suitable conditions for survival is usually first based on the pH. The tolerance range of plants is usually somewhat larger than that of animals.

The pH is measured on a logarithmic scale with values from 1 to 14. Water levels in the aquarium are from 4.5 to 9.5, whereby the two extremes. A pH of 7 is considered neutral, i.e. neither alkaline nor acidic. Logarithmic here means that water with a pH of 6 already contains ten times more acid as water with a pH of 7. Water with a pH value of 5 is, as such, one hundred times more acidic that water with a value of 7. So-called black-water aquariums, which South American fish such as scalars or the often-held red neon thrive in very well, have pH values ranging from 5.5 to 6.5.

Aquatic plants thrive best in aquariums with a pH below 7. This is because at these values carbon dioxide value is higher, which in general is important for plant growth. East African perch do especially well in water with a pH above 7, which is referred to as alkaline.