Hi, I have emailed someone from Pet Remedy however not sure when they will get back to me, Meanwhile if anyone can come back to me on it from here, be appreciative as not sure whether to continue using the plugs I have. 'Hi I got your email address from a post on Facebook as I would like something clarified in the Precautions. 'Do not use plug with more than two refill bottles before replacing.' I have been using this product for the past 5 months as we had a new addition to settle in. This is more effective than the other recognised one on the market. I have one plug upstairs, one downstairs. However I just put the third refill in and saw this precaution. I am not sure whether it implies that I cannot use the existing plugs and need to purchase new plugs? Thanks for your help'