As a general rule, there should be no metal in an aquarium or pond water. Many metals have the property of releasing free metal ions (loaded particles) into the water, which have a toxic effect on invertebrates, fish and microorganisms. The more acetic the water (pH less than 7), the larger the percentage of dissolved metal ions in the water. An extreme situation occurs when there is (acid) rain and the rain water collects in the gutters and is used: The low pH value of the rain water can dissolve larger amounts of copper ions from the gutters which are usually made of copper, thereby leading to poisoning symptoms. The use of a good water conditioner leads to the binding (chelation) of metal ions. If symptoms of poisoning are observed, a water change is needed (nevertheless). Observe caution with tap water: Tap water often contains lead, copper or zinc (from the pipe system). Therefore, it is imperative to use a good water conditioner when doing a water change! The use of hot water boilers can also cause problems.