Metal Halides Vs. T5 HO Lights: Leveling the Playing Field “Can you really grow SPS under T5s?” This seems to be a daily conversation starter with customers who walk into Elite Reef and notice the 75 gallon SPS display with only T5s running on it. This article will attempt to put that question to rest and level the playing field between halides and T5 HO fixtures. I would first like to establish the context in which I’m comparing these two very different lighting systems. For the T5 side of this comparison, I will be referring to our 75 gallon hard coral reef at Elite Reef. We are running a Tek Light Elite 6 bulb fixture running the following Geissman bulbs: 2 actinic blues, 1 pure actinic and 3 aquablues. It is important to keep in mind when considering the results of this article that Geissman bulbs are one of the best for PAR output and color in the industry, so if you are trying for similar results this is an upgrade that should be considered. It is also important to note that Tek Light T5 systems are known to sport some of the best reflector systems, and therefore throw quite a bit more light than some lower end fixtures. The MH opponent for this comparison will be my personal tank with a 250 watt Ushio lamp running on an Icecap ballast. Ushios are also known in MH circles as one of the top performers, so this should be a good comparison between light sources. For the final and most important aspect for this comparison we come to the corals themselves, and the conditions in which they live. My personal tank (MH) is primarily a SPS reef and is the source of the majority of the coral in our shop hard coral display (T5). The two tanks also share nearly the same depth, and both are running similar flow patterns with their Vortech MP10s. I personally maintain both reefs and strive to keep water parameters at similar levels in both tanks to make transitioning frags between the two systems easy. I realize that this is still far from scientific, but with this context established it should be quite easy to draw some comparatives from observation of coral growth. Lets get down to the fun part. The coral: Stylophora (Finger Coral) Frags of this SPS were obtained from Elite Reef for both systems approximately five months ago, and both have shown amazing growth rates. Two frags were placed high in the shop system (T5), and one frag was placed high in my personal system (MH). The frags in the shop system are growing at approximately ¾” per month in a loose pattern as an indication of their local flow. The frag in my personal system is growing in a tighter formation due to more flow, but growth rates appear to be similar. Seriatopora Hystrix (Birdsnest) These frags were also obtained from Elite Reef about five months ago and were both placed low in the tank under medium high flow. Both frags have shown extremely similar formation and growth rates at about 1” per month. Acropora Nobilis This coral was acquired as a colony from Elite and a large portion was fragged for the shop system. To my surprise this one has shown very little growth in my own system but within a couple of months in the shop system as fully encrusted and began to expand its base. Both pieces are located fairly low in their tanks and in similar flow patterns. Acropora Secale This species started out as a frag in my system over a year ago and has since grown to be a healthy softball sized colony. A frag from the colony was placed in the shop system about five months ago, and it has since shown some great growth as it covers its frag plug. Growth rates are hard to compare due to the size and health of the mother colony, but I will not be shocked when the new frag catches up. This list could continue on through an endless list of SPS and LPS species that have had great success under both the metal halide system and the T5 system, but the end result would look like what we have already seen. The T5s have without fail shown either similar or superior growth rates on any coral I can throw at them, and to top it off they do it with the following advantages: Lower fixture costs: Comparable T5 fixtures typically cost about half of what their halide counterparts do. Running Costs: Halide fixtures are also typically higher wattage fixtures with less efficient reflectors. Heat: Metal halides throw much more heat than T5s and in some cases may need a chiller to combat this problem. Color mixing: T5 lamps come in higher variety than halides which gives you more control over the look of your reef. This article should not be seen in any way as an attempt to devalue metal halide lighting, because the result of such lighting systems is undeniable. They grow coral at amazing rates and give a shimmer effect that can be matched by nothing, but it should be realized that T5s are only getting better, and with the proper bulbs growth rates similar to halides are easily attained.