I Was give over a year ago a bottle of this product,so i have used it for that period of time,no smells or signs of any problems,I cleaned the water but then just followed the instructions on the bottle that easy, [bottle returned]
I use this regularly to prevent the water in our waterbutt from smelling horrible. Thankfully it works reasonably well even if you don’t clean out the butt and start with fresh water (not my favourite job!)
When spring came around, I checked my rainfall butt and found the water therein not only stagnant but pretty rank too.
Having turned the water out and cleaned the butt inside, I refilled it and added a dose of this Defenders treatment. Since then, the water's be clear and fresh-smelling. I look forward to watering the garden now.