The JBL ProAqua Test CO2/pH Permanent is a beautifully designed unit for attaching inside the aquarium which permanently displays the pH value or the CO2 content of the aquarium water. Two separate colour scales, one for pH and the other for CO2, are included with the unit to be attached to the pane of the aquarium, as required.Why test? Carbon dioxide (CO2) is the most important plant nutrient. The consumption of CO2 differs from aquarium to aquarium and depends, amongst other things, on the following factors: number and demands of plants, carbonate hardness, water movement and light. Fertilisation with CO2 is usually done with a CO2 fertiliser system. In the aquarium water, a CO2 content between 15 and 30 mg/l is recommended. This range is safe for fish and at the same time ensures luxuriant plant growth. 20-25 mg/l CO2 has proven to be ideal. In special aquariums with a large number of plants, so-called scapes, higher values of up to 35 mg/l may be required. With this test you can d