A frag tank is a working tank with characteristics of function over form, practical, and above all produces results. If you are planning on taking cuttings (frags) from colonies in your main display, you will want them to put a base down on a frag plug quickly (if not quicker) than it did in the display. So if you want to replant them, sell them online, or swap them with other reefers let’s check out some basics on how to set up a frag tank.
The tank can be any size, but since it is only for frags, a few factors should be taken into consideration. First, you need an area large enough for placement of frags, frag racks or egg crate, so choose a tank that is both wide and long for maximum surface area. Second, the tank can be shallow in height, even as low as six inches top to bottom, which will still give plenty of room for frags to grow upward while providing super easy access. So, don’t knock a 3′ x 2′ x 6″ tank, because it could hold literally hundreds of frags while still being easy to maintain, light and power. Third, an open-topped, rimless design is best to give better access for sheets of egg crate to be lifted in and out with ease. Fourth, there’s no need for thick glass tanks, which presents a cost-saving, however, shallow acrylic frag tanks may still need a euro brace to keep them from bowing along the front.
Opt for a rear filtration chamber like a typical All-In-One (AIO) marine tank, which makes the system self-contained and able to sit on a counter. Otherwise, with a little drilling, an overflow box can be installed to most aquariums and plumbed to lead to a sump inside a cabinet below. If an sump filtration is considered, a standard sized frag tank (typically with a footprint of 24″ x 18″ or 48″ x 24″) would have no problem pairing with a cabinet and sump.
Although not filtering a tank full of fish, your filtration system should be sufficient to cleanse the water well enough to a standard of keeping SPS frags. Using filter socks or filter pads for mechanical, ceramics for biological, carbon and GFO for chemical filtration.
Additional filtration like skimmers can help maintain pH via oxygenation, however some deem them unnecessary because they potentially skim off the coral food and trace elements. Algae refugiums and algae scrubbers aren’t necessary as there won’t be enough nitrate in the frag system to fertilize them and they will compete for elements like Iron.
Lighting a wide area of frags can require an even spread front to back and left to right across the frag tank, with no hot spots or shadows. T5 lighting is a popular choice for this and can result in fast growth. Another option would be to use multiple, linear LED strips (like Reef Brites) to acheive a wide spread and even par distribution, delivering light and energy to all the frags in the tank. If you have to use spotlight style LEDs, mount them higher to get a wider distribution of light.
If moving a lot of frags from your main tank to your frag tank its a good idea to use the same lighting, only arm yourself with a PAR meter and adjust the frag lights so that the frags are getting the same PAR as they were in the much deeper display tank.
Water movement should be even like the lighting, so use wide outlet wave-making pumps which won’t strip the flesh off the corals next to them or cause dead spots at the other end of the tank. Gyre pumps are good for long shallow frag tanks, or even a homemade spray bar connected to a simple pump or sump return. Delicate frags that prefer less movement like mushrooms or zoas may only need the flow from the return pump
Hard coral frag tanks will use up a lot of buffers and elements, so auto-dosing or a calcium reactor will be necessary to supply them the building blocks they need. You’ll also need test kits for Alkalinity, Calcium, Magnesium, nitrate and phosphate. A four way dosing tube holder (e.g Bubble Magus) will be necessary to clamp hoses to a sump or the back chamber of an AIO.
Decor should be absent in the frag tank set up, with hygiene being the priority. Leave a sand bed out and go for a bare bottom instead which is easier to keep clean and won’t collect detritus like sand will. Bare bottom also means that you can direct powerful currents under the frag rack to keep detritus in suspension and ensure adequate flow around all the frags.
Fish and inverts should only be added if they do a beneficial job, so a tang or Foxface could be added to large frag trays to control algae, along with a wrasse to control pests. Clean up crew like hermits and snails can be used to control algae in smaller tanks, with Emerald crabs, Peppermint shrimp, Urchins and Sea hares on hand to do specific tasks if needed.
Don’t double up the tank as a fish quarantine or hospital tank as fish-only medications and inverts don’t mix. Catching fish can be problematic too as often they will hide under egg crate, causing you to lift it all out to catch a fish.
These are just a few tips on how to set up a frag tank to get you started.