You have probably heard it said many times that bio balls which are used in Wet/Dry Trickle filters are "nitrate factories" or that someone's bio balls have "gone bad". Bio balls are a great nitrifying bacteria platform but, like any other filter media, they can produce nitrates, if not maintained. Curing the problem is simple, costs nothing and takes only a few minutes.
More: Wet/Dry Trickle Filters have been around for a while. Providing a large surface area for great nitrifying bacteria platform, they also do a great job of oxygenating your aquarium water.. Read more
More: DIY Wet/Dry (Trickle) Filters come in many shapes and sizes and can be easily constructed of a wide variety of materials.