What Is A Frag Tank For?
Frag tanks have been growing in popularity in the saltwater aquarium hobby. When I began keeping saltwater aquariums in the mid 2000’s frag tanks and frags in general were only beginning to be collected and traded. Today the reefing hobby is dominated by coral frags as opposed to coral colonies.
coral frags can ruin the aesthetic look of a saltwater aquarium
A place to store fragged corals
For hobbyists with successful systems that are growing corals and farming them , frag tank provide a space to house them. Main displays can quickly become cluttered with hundreds of frags , ruining the asethic appearance with a clutter of frags and frag racks. Frag tanks are really the perfect option for housing them. Reef casa frags tanks are super easy to set up next to existing displays. The glass is non tempered so some even drill them and connect them to their main aquarium for easy of maintenance.
Frag Swaps
If your attending a frag swap or trade show with corals you need a frag tank. There is no easier way to transport and display corals for sale than a frag tank.
A place to grow frags
Hobbyists with larger systems in some cases would like grow out frags before placing them in their main system. A single polyp of high end zoathid for example can easily be lost in a 150+ gallon aquarium. A frag tanks gives can provide a safe space for the coral to grow out before introducing it
Even small frag tanks can be useful for this application an set up next to existing tanks. 
Even small frag tanks can be useful for this application an set up next to existing tanks.
A place to quarantine
For hobbyists with larger valuable coral collections its risky to add to new frags because of the potential of introducing unwanted pests. Frag tanks provide a space to house and monitor new corals frags for issues before taking the leap into the main system.
Collecting
Frag tanks are a really great way to easily organize and collect frags. Keeping just a frag tank and no display tank was once unheard of. In today’s saltwater aquarium market its not uncommon for hobbyists to enjoy collecting and growing coral frags without keeping a traditional reef system.