The ModMag is the cornerstone many solutions in the AvidAqua line of aquarium products. Its sliding-slot design provides magnetic attachment of multiple accessories, simultaneously, both inside and outside an aquarium. Since they first hit the market, there have not been significant improvements in magnetic attachment designs for reef aquariums. The ModMag changes all that with innovative new features and extra strong magnets that make it hold tight while also staying reef safe. Others are made with acrylic, sealed with glue, and fragile. Over time, and without your knowledge, the acrylic swells, glue fails, saltwater gets inside, corrodes the magnet, and then heavy-metal toxins leach into your tank. Don't put your entire reef and beloved animals at risk! The ModMag is instead made from durable, inert, pliable ABS plastic, and is ultrasonically welded and redundantly double-sealed against water intrusion - using no glue. Two pieces essentially become one when assembled. It can be used either to mount AvidAqua accessories like frag racks, probe holders, camera mounts, etc., or you attach your own DIY or 3rd party add ons. The uses on an aquarium are almost endless! Use with ModMag Accessories