Dr. Dryden's Activate filter media is a wonderful product I like to use when installing a new sand filter as an alternative to silica sand. Dr. Dryden, a marine biologist, invented the glass media to improve the lives and life span of marine animals held in captivity. He proved that these marine animals were experiencing lung infections and dying sooner in captivity than the animals living in the wild. This was due to the animals breathing the chloramine gas above the surface of the water. Chloramines come from the combination of the chlorine disinfectant (chlorine produced by a salt system, or chlorine tabs, or chlorine shock) and the perspiration, body oils and urine from swimmers. Chloramines then off gas into the air just above the water. I use products like Zeo sand that also traps ammonia particles that produce chloramines, but this product is even more effective.
Activated glass media, or AGM, is 300x more effective than silica sand for pool filters. This media requires less backwashes and less water to clean the filter. It traps particles as small as DE filters, but does not need to be recharged with DE powder, a known carcinogen that is expelled into the yard when a backwash is done and turns to loose white dust once dry.
The media comes in two sizes, coarse and fine. The course media is put in first, which is larger and provides better water flow around the laterals of the filter (the arms inside the filter that allow clean water to flow back to the pool) and the fine, which goes on top. The glass is not sharp, and is treated to have a negative charge; it's actually electromagnetic. This keeps any dirt from sticking to the glass itself and reduces the amount of water required for doing a backwash. AGM prevents biofilm from forming inside the filter (a thin, slimy film of bacteria that adheres to a surface) thus reducing the chlorine demand and algae growth.
Because of the electromagnetic charge, dirt does not stick to the glass and clump up like silica sand, creating wormhole channels inside the filter that reduces the filters ability to function (and reduces water circulation). These benefits continue, because it never has to be replaced. Once added when the filter is installed, it will last as long as the filter and never needs to be replaced (ever). It is not an inexpensive media and one I dont use on old filters when changing sand. However when added during a new filter installation, this media will save you money over the life of the filter. Savings in water, using less to backwash and having to backwash less frequently, and it eliminates the need for sand changes. Normal silica sand is effective up to 5 years. Never having to replace the media saves you money in labor costs and the cost of replacing sand.