Water Conditioner Guide
What a water conditioner does, how it neutralizes chlorine and chloramine, why chloramine needs treatment, and how to dose it correctly.
What it is
A water conditioner, also called a dechlorinator, is a liquid treatment whose main purpose is to break down chlorine and chloramine and make tap water safe for fish to inhabit. Municipal water utilities add these disinfectants to make drinking water safe for people, but they are harmful to fish and to the beneficial bacteria in an aquarium, so the water must be treated before it enters the tank.
How it works
The standard active ingredient is sodium thiosulfate, which reacts with chlorine and chloramine to form harmless byproducts. Sodium thiosulfate appears as a rock-salt-like white powder and is dissolved in water to make the liquid product. Chlorine is fairly unstable and will gradually evaporate from standing water, but chloramine — a more stable disinfectant made by combining ammonia and chlorine — cannot be easily removed by evaporation and must be neutralized with a conditioner.
Ammonia handling
When a dechlorinator breaks the chloramine bond it neutralizes the chlorine portion but can leave behind toxic ammonia. Some formulas add chemicals that temporarily lock up the ammonia into an inert state (as ammonium) for up to 24 hours, giving the biological filter time to process it.
Types and variants
- Basic dechlorinators: neutralize chlorine and chloramine only
- Ammonia-detoxifying formulas: also bind ammonia temporarily
- Multi-function conditioners: may include pH buffers or slime-coat additives such as aloe vera
Choosing and dosing
Because chlorine levels vary by municipality, following the package dose is essential; a typical concentrate uses on the order of 1 ml per 10 gallons of water. Some formulations allow dosing up to five times the recommended amount within a 24-hour span, which gives a safety margin.
How to use it
It takes about 2-5 minutes for chlorine and chloramine to be neutralized, so many manufacturers advise dosing the tap water in a separate container before adding it to the aquarium rather than relying on the reaction to finish inside the tank. Conditioner is added with every water change and whenever new tap water enters the system, including after large top-offs. When dosing directly into the tank, distributing the conditioner across the water flow helps it disperse quickly before the new water reaches sensitive livestock.