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Many freshwater fish come from regions with pH between 6 and 7.5, and will tolerate living in values slightly outside this. Many livebearers find our water ideal, and although tetras and rasboras will live in our water, breeding may involve conditions more like where they are from. Chocolate gouramis and parosphromenus species need acidic water pH 5-6. Discus prefer around 6. Rift lakes cichlids on the other hand like it alkaline around 8, and so our water is ok for them as far as pH is concerned. Seawater has a pH of around 8.
Some fish have been bred commercially in ponds for generations, and may well have adjusted to different values.
What affects pH?
Wood can reduce pH, CO2 addition will reduce pH as may peat extracts and 'black water' tonics. Some stones are likely to raise it, those found in aquarium shops shouldn't to any degree.
Intense light, including afternoon sunshine, on an aquarium may cause an increase in photosysnthesis, levels of carbon dioxide/ hydrogen carbonate may decrease, and the pH may rise significantly.
KH
this is 'carbonate hardness' but can also be seen as buffer capacity, since it binds with acidity, stabilising the water's pH. This one reacts with acids stopping a rapid drop in pH. It used to also be called temporary hardness, since it can be removed by boiling. This is the scale deposited in boilers and kettles.
Ca(HCO3)2 --boiling --> CaCO3 + H2O + CO2
GH
standing for 'general' hardness or 'GesamtHärte', this is the total [Ca+] and [Mg+] in water. Apart from these Calcium and Magnesium ions, there are one or two others present in such small amounts that we can safely ignore them. The part of the total hardness includes that which cannot be removed by boiling, and has been called 'permanent' hardness.
Conductivity
Mentioned in older books but not considered for the home aquarist because of the cost. Nowadays a small digital meter will cost below 30€. Water is a good solvent. On its way to us, it dissolves small amounts of minerals. Some rock formations such as chalk will contain calcium and magnesium, whereas others such as granite and lava will not. The dissolved substances are present as and ions. These electrically charged particles will move in water when a voltage is applied, how much current flows corresponds to the quantity of minerals dissolved. BUT this means all minerals, not just those causing hardness.
Aquarium water starts off with the same conductivity as tap water. Between 600 and 1000 µS in Berlin. Reverse osmosis water has a conductivity of 10µS. Fish waste, fish food, water conditioners, fertilisers and other additives can change these values. Other things being equal, a significant rise would indicate it's time for your regular water change (max 30%).
The Nitrogen Cycle and the Aquarium
Nitrogen is essential to life. Plants take it up, helped by bacteria, animals eat plants, animals die and decompose, and bacteria free nitrogen again. This is 100 times simplified. What happens in aquariums, being at least a partially closed system, is an incomplete version of this.
Tests
- Combi test strips- the least accurate but the most convenient for a quick overview. Stick to well known makes and you'll get 6 or 7 parameters measured all at once. Good value.
- Liquid tests- can be selected according to the pH range required. Thes are made of combinations of special dyes called 'indicators' which change colour at particular pH values. Other tests rely on a colour change due to a chemical reaction. Some of the reagents may be caustic or be harmful in other ways. Read the instructions from beginning to end before use.
- pH meters- very good but only as accurate as their maintenance and calibration, electrodes do not last for ever. Conductivity meters, very accurate if kept clean.
Terms used:
Other Values
Sorry, not that far yet.