The BioStone Plus is used in Filter Position 2 (right). The mid range filter is designed with compressed carbon block and is enriched with Plus Technology, by adding specialty media to to the carbon block to increase contaminant reduction. It removes Chloramine, heavy metals and other tough contaminants better than the BioStone Basic. Will not remove heavy metals as well as the UltraWater filter does. Containing Scale Guard protection, it will outperform any GAC filter – regardless of micron rating.