Walter T., vinegar can be added to the media once a year in amounts of 1 cup white vinegar to 3 gallons of water. My circulating water bog is working fine. There has been NO media change with this bog in 17 years, and all the VFT's, ping's, and drosera, along with the sarracenia, are just great. Best of all, though the tray system works, it is an easy way to culture rot in your plants. Constant media change is not the way I wanted to grow plants, so I made a bog that works like one in nature. I do plan to make a bigger one and retire the old, but that will be its first and only media change, ever.