Starting with compressed carbon block, we add Plus Technology by impregnating it with specialty media to increase contaminant reduction. The carbon block water filter cartridge 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. This Athena filter is used in Filter 2 position for the Athena Classic. Also good for most older models – if unsure please call Customer Service. Rated for 1000 gals. Free Shipping.