Best Practice Guide to Eco-Safe Water Changes

For hobbyists, disposal of water from our regular water changes requires some care to help 

prevent spread of aquatic diseases in New Zealand waterways. 

In an ideal world, it is best not to dispose of untreated waste water down the drain as it goes 

directly into our waterways. Ideally, you should always treat waste water with a disinfectant 

like chlorine bleach (Janola) to kill bacteria and viruses. As chlorine is highly toxic to fishes, 

chlorine should never be added directly to the aquarium unless the tank is completely empty 

of livestock. 

To disinfect waste water, remove water into a holding barrel and add 5mls of bleach per litre 

of water (or 1-5mg/L). Let the water sit in the barrel for about an hour. After the hour has 

passed, the water is then then safe to dispose of down the drain. If you wish to use the water 

on your lawn or ornamental garden instead, you can add a dechlorinator like Seachem 

Prime after the hour has passed, then just pour the water out onto the lawn as needed. 

If you are not able to dechlorinate your tank water, try to avoid disposing of water down the 

drain as this will risk spreading aquatic disease in our waterways. Instead, freshwater can 

safely be added to your ornamental garden or lawn (but avoid adding it to your vegetable 

garden or disposing of it near drains or waterways).