I'm using Tetra AquaSafe + for monthly maintence & as dechlorinator for tap water... Expiration date 06/2017 When I change about 40% of water I add needed ammount recommended on bottle (for ~130L add 15ml of stuff) & water smells ok. In couple of hours it start to stink very strongly. Like something dying in my aquarium. The smell lasts for about 3-4h making room with aquarium just nasty smelling. Is this normal?? Something not right with my tap water or with water conditioner?

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