daro products dangerous

I recently purchased de chlorinator from Westpack with the name Grants (distributed by Daro). It was the 1st time using the above product and ion Tuesday (10.11.2020) my son did a water change using the product and it has killed 80% of my fish population (koi, goldfish, guppies and two other fish that I have had for about 3 years). I have called Daro and explained to them the situation and are still awaiting a response from them. Please do not purchase the above product if you care about your fish pets. I was so sad to have to bury these fish., some even had their lungs explode. Daro needs to be accountable for this mess. I have sent an email to jenny wit still no reply.