I added an
additional 120 lbs of Caribsea Arag-Alive Special Grade Reef to my used 125 gallon tank after I bought it. It specifically states on the bag: "Never needs replacing. Unlike limestone and dolomite, Arag-Alive! remains chemically active for the life of the aquarium."
In addition to the sand in the tank, I set up a 30 gallon tub with 120 lbs of play sand from Lowe's. It's over a foot deep, with a slow flow of water over it. Water enters one end of the tub, and exits on the other. A nozzle spreads the flow, and three bulkheads keep the flow evenly dispersed. The tub stays covered, and no light ever gets in. I used to dose this DSB with NO3 : PO4 - X until it got a substantial, and sustainable level of bacteria built up. I no longer dose my tank (been almost a year since I stopped), and if I'm feeling frisky, I might do a 10% water change every couple of months or so. NO3 is non-detectable, and PO4 is <.04 ppm. Several months ago, I removed the Miracle Mud from my refugium and put in 40 lbs of Arag-Alive! Fiji Pink sand. My 40B has 60 lbs of Fiji Pink sand in it also, and both tanks share the same water. Between the two tanks, remote DSB, and refugium, I have roughly 370 lbs of sand to filter approximately 150 gallons of water. My parameters are rock steady, and I attribute it mainly to the natural filtration all that sand offers. Sure, I have live rocks as well, but
far more sand. Just my 2c...