The pH value indicates whether aquarium water in an acid, neutral or alkaline/base condition. It shows the concentration of certain ions which are responsible for alkaline/acid reactions.

pH value starts from 0 to 14. pH < 7 called acid, pH > 7 called base/alkaline, pH = 7 called neutral. pH is valued by logarithm scale, therefore one point fluctuation in pH value = 10x alteration in the ions responsible for the change.

Any change in pH value is stressful for aquatic life (fish, aquatic plants and microorganism), while sudden drop in pH value can kill them.
For aquarium keepers, maintaining aquarium pH level around 7 is recommended since most freshwater fish and aquatic plants can only be survive in pH range 6-8. But some pH requirements for fishes are different, it depend on the fish orign. For example : some species like African chichilds require pH around 8-8.5 while South American chichilds prefer slightly acid water (pH around 6.5). So, it's very important to check the pH-requirements for each of your future pet fishes before making decision about combination of fishes for your community tank!.

How to control aquarium pH ?
Using CO2 generator and regulator to maintain pH at a desired level. CO2 need is highly depend on pH level and Carbonate Hardness (KH) level. The use of CO2 is the most natural method of all methods in regulating aquarium pH level. Please see CO2-pH-KH relationship table for CO2 level adjustment and our guide to CO2 system kits for the health of your planted aquarium.

Aquarium pH and Aquarium Cycle
pH value has direct impact on the toxicity of total-ammonium compounnds (NH3+NH4) in the water. With pH value around/ below 7, ammonia (NH3) presents in the form of ammonium (NH4) which is largely non-toxic to fish. The higher the pH value, the more highly toxic ammonia (NH3) is generated from total-ammonium compounds.
In the long run, any cause of the ammonia and ammonium enrichment must be eliminated.

Total Ammonium - pH - Temperature
For certain aquarium pH level, increasing temperature leads to increasing total-ammonium compound in the water. So keeping aquarium temperature stable is important for aquarium cycle process. Please see our Ammonia-pH-Temperature relationship table for your guide.

Frequent Water Changes
Frequent water changes is important to reduce build-up nutrients such as Nitrate and Phosphate. But you should pay attention to fluctuating water parameters such as pH and temperature that are associated with water changes which can cause undue stress on your organisms. There are some concerns about the source of water :

• Tap Water in the U.S.
Tap water pH is adjusted by local water treatment centers to ensure that minerals present in natural water sources do not deposit in pipes and water meters. Calcium compounds for instance that are are present in most lakes and streams will precipitate out if water becomes acidic, that is the pH drops below 7.0.
To prevent acid water corrode plumbing systems, water treatment centers add base chemicals to the water supply to make it more alkaline. Thus in most regions on the country tap water is alkaline with a pH of about 8.1.

The Tap water also contains a significant amount of trace elements and potentially harmful chemicals such as chlorine, heavy metals, phosphates, and nitrates!
To remove them, you can use Water Purification filters such as Reverse Osmosis / Deionizer filter, UV Sterilizer and Ozonizer.
Reverse Osmosis strips everything out of the water-the bad, but also the good. Healthy minerals are eliminated as the natural levels in water are altered and the water is now acidic!

• Well Water in the U.S
Unlike public water supplies, the Environmental Protection Agency does not regulate private ground water wells. Consequently, it is the responsibility of homeowners to monitor the quality of their well water. Low pH (acid water) typically found on private well water, it can corrode plumbing systems!.

Water pH is only one of many factors influencing well water quality. Well water should be tested once a year for total coliform bacteria, nitrates and total dissolved solids, as well as pH.

• Distilled Water in the U.S
Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.
Distilled water purchased from a store will have a pH of less than 7.0, often nearer 6.0. This is because after distillation it has been exposed to air, and air contains CO2 which readily dissolves in distilled water and causes a reduced pH.
Only Freshly boiled distilled water (and protected from CO2 during cooling) will be pH 7.0.

• Drinking water in the U.S
An ideal pH level for drinking water is 9.5 [the higher the pH level, the ORP (antioxidant level), and mineral content in water, the more benefits the body will receive].
But some tests reveal that most of the best-known bottle water brands in the world had a pH level below 7.0, meaning they actually are acidic.
The age of bottled water affects its pH level, as do changes in temperature and exposure to air.

Note:
Bottled water is drinking water, carbonated water, mineral water, distilled water, or de-ionized water packaged in plastic bottles or glass bottles.
The FDA tests bottled water for impurities, it is not required to monitor the water's pH level.