Red Sea Freshwater pH Low Lab Test

Introduction to pH
pH is a measure of the acidity or basicity of water and is a very important parameter in the biology of aquatic organisms. The scale runs from zero to 14. Zero is the most acidic and 14 is the most basic. The pH scale is not linear but logarithmic, therefore a change of 1 pH unit, for example from 7 to 6 means that the water is 10 times more acidic. 

pH values in natural waters around the world vary considerably: from acid South American Jungle streams (pH 5-7) to alkaline African lakes (pH 8-9). 

Many fish species have adapted to a wide pH range and are therefore not demanding with regards to the pH value in the aquarium. Some species, however, have only adapted to a very narrow pH range and as a result of this may require a specific pH value in the aquarium. This is especially important when one wants to breed these fishes. Many freshwater fish species have been bred in captivity for several generations, such that their natural pH preference for reproduction may have disappeared. On the other hand, wild caught fishes are still being imported. To know the specific requirements for your fish you should consult a reference book and your fish dealer. 

The pH is also important for growing water plants. Above pH 8 most aquarium plants are unable to grow, since this pH value prevents the uptake of CO2. 

The most favorable pH range for freshwater plants is pH 6.4-7.2. 


The pH of the aquarium water influences the chemical form of certain dissolved compounds. This phenomenon is especially important in the case of Ammonia. This waste product of fish can exist as relatively harmless Ammonium ions (NH4+), or as toxic Ammonia (NH3). At a higher pH the percentage of toxic Ammonia increases, making Ammonia toxicity a more serious threat than in water with a lower pH. 


Tap Water 

The composition of tap water varies enormously from location to location depending on the source of the water, treatment process etc. Before adding tap water to an aquarium all of the parameters (i.e. pH, Hardness, Chlorine) should be checked for their suitability for the particular application. 

Information regarding hardness and Chlorine is available with Red Sea’s Hardness and Chlorine Fresh Lab-Tests. 


Adjusting pH 

The pH of tap water can be increased or decreased by using one of the chemical pH adjusters available on the market. 

Chemical adjusters should never be added directly to the aquarium as sudden pH changes can be stressful to fish and other aquatic organisms. Use a mixing vessel to prepare tap water to be added to the aquarium. 

Alternatively, pH can be adjusted by natural methods: 

To reduce pH, filter over peat or add CO2. 

To increase pH, filter over Calcium Carbonate. 

Note: Over time the pH in an aquarium decreases due to natural causes (i.e. CO2 production by bacteria). When reducing pH it is advisable to reduce the pH to 0.5 units above the desired level. 

Pictured: Both Low and High pH Tests