Similar fish deaths were recorded when Hastings District Council (HDC) introduced low chlorine levels to the town’s water supply in 2015 in an effort to prevent an outbreak of E. coli in Havelock North.
Hicks said he believed increased chlorine levels killed fish then, and again a fortnight ago.
“There are about 400 fish in the pond and this has happened to me before. It’s the chlorine in the water that’s killed them.
“We all know there is chlorine in the water, but I believe at times it is stronger.”
After one previous spate of fish deaths, Hicks said the council reimbursed him and told him it would inform him if there were any significant fluctuations in future chlorine levels.
He said “dribbling” the water into his pond for a top-up was likely to be the only way to guarantee the safety of his fish, but this was impractical.
An HDC spokesperson said chlorine was added to the drinking water supply network to ensure public safety, as required by national water regulator Taumata Arowai.
“Public advisories are not common practice due to chlorination of the supply being permanent and chlorine levels remaining relatively stable.
“Fish have a very low tolerance to chlorine, meaning chlorinated drinking water generally requires treatment to make it suitable for fish to be kept in.
“We advise that people should contact their fish supplier or a specialist to find out the optimum conditions for fish to be kept in.”
The spokesperson said HDC routinely tested its drinking water for contaminants and chlorine levels to ensure they remained within operational targets.
“The sampling and testing is carried out by an IANZ-accredited laboratory with field sampling results available immediately and bacteriological results after 18 hours.
“The combination of manual sampling and online continuous monitoring allows council to detect and respond quickly to any changes in water quality. The results of this monitoring are not publicly accessible.”
A Taumata Arowai spokeswoman said the amount of chlorine in drinking water when it left a treatment plant would normally be between 0.2 and 1 milligrams per litre.
“That means there’d be around one drop of chlorine in a standard bathtub [150 litres] full of water.
“New Zealand’s drinking water standards set the maximum acceptable value (MAV) for chlorine at 5mg/l.”
She advised people to talk to their water supplier if they had questions about their water.
“Chlorine can be toxic to fish, other aquatic animals, reptiles and amphibians. That’s because, unlike people and other household pets, these types of animals absorb water directly into their bloodstream.
“For these pets, chlorine can be removed from water by letting it sit out for a few days or by buying a product at your local pet store that removes the chlorine.”
SPCA national science manager Jessica Walker said the best way to fill goldfish ponds or aquariums was to allow the water to sit so the chlorine could “gas off” before any fish were placed in it.
“Aquarium water conditioner can also be used to neutralise the chlorine in the water,” she said.
Mitchell Hageman joined Hawke’s Bay Today in January 2023. From his Napier base, he writes regularly on social issues, arts and culture, and the community.
