I have used Botanicare Hydroguard to keep a healthy mix of bacteria that along with air will keep a batch of water with nutrients from turning into a smelly mess that will kill or harm your roots, fish, ect.. This involves live bacteria and their spores. Every bottle has a manufacture date and the instructions that it is good for 6 months after opening. I have seen pictures of bottles that had altered dates and in my case bottles that had no date at all. I took the bottle that you see with the date and was able to wipe it off the date without any damage to the label.