How often should I use aquarium water conditioner?
Use it every time you add untreated tap water to the aquarium, including during water changes, setting up a new tank, and topping it off. Use a dose for the amount of new water (not the tank's total capacity), and follow the label's instructions if your tap water has chloramine. If you use preconditioned water or RO/DI water that has been treated, a dechlorinator may not be needed.
How can I tell if aquarium water conditioner has gone bad?
First, check the bottle for an expiration or best-by date. But no matter the date, throw it out if you notice a strong or unusual smell, unexpected color change, clumping, or separation that does not remix when shaken. Also discard it if it no longer seems to be working, like if you notice a chlorine smell after dosing. To extend its shelf life, store it tightly sealed at room temperature and away from heat and light, and avoid contaminating the cap or dropper.