I’ve had my 180 gallon tank for around 14 months now and have been using the power compact lights that came with the tank. The original lighting consisted of 6 - 96 watt bulbs. I used 4 – 10K bulbs and 2-Dual Actinic bulbs. The lights were about 2 inches from the water surface. The tank always looked quite bright all the way to the bottom.
Contrary to popular opinion, you can grow SPS corals under PC lights – you just need to keep the lights close to the water and the corals high in the tank. In the 12 months since I’ve been putting corals into the tank, I’ve only lost one coral – a short tentacle plate coral. I don’t really know why this coral died, but it slowly wasted away over a period of about a month and certainly could have been due to a lack of intense light.
I’ve been thinking about switching to metal halides for quite a while now but really wanted to get through the summer heat before I went and added new lighting. I did a lot of research on-line to try to come up with a plan for upgrading. In late October, my local fish store had a pair of 400 watt DE fixtures and ballasts that he was willing to sell for a very good price. So, I went ahead and bought them and started planning on a way to mount them.
The canopy that came with the tank was only about 4” tall – just enough to house the PC lights. Obviously that wasn’t going to work so I began building a new canopy. I ended up using some 1x2 and 1x4 lumber for the framing and covered this with ½” oak plywood. I got some oak doors used for kitchen cabinets and used them to close up the front of the canopy. The inside of the canopy was painted gloss white and the outside was stained to match the oak stand that the tank is sitting on.
Inside of the canopy, I fashioned mounting rails for the metal halide lights that would keep them as high as possible so that I could slowly acclimate the corals to the new light. The fixtures are approximately 14” from the surface of the water. I tried orienting the fixtures a few different ways and determined that the best light coverage was achieved when the reflectors were mounted parallel to the front of the tank.
In addition to the metal halides, I also installed 4 - 36 “ fluorescent tubes. I mounted two along the front and two along the back of the canopy using reflectors salvaged from some old fixtures that I had lying around. These bulbs are going to be used as supplemental lighting so that I can view the tank without firing up the metal halides.
Once everything was assembled and wired up, I turned the lights on. I turned the fluorescents on first and, as expected, they are rather dim. They provide enough light to view the tank but are definitely not adequate to get anything growing.
I then fired up the metal halides. After a 5-10 minute warm up period, the tank started glowing with color. The 20K bulbs really highlight the colors of the corals and are almost like bright actinic bulbs. The bulbs burn with a nice blue color and produce very defined glitter lines on the sandy bottom. Somewhat surprisingly, they actually look dimmer than the original PC lights. I’m guessing that this is largely due to the difference in the color of the bulbs and that a 10K or 14K bulb would really brighten things up. This isn’t a problem for me because I actually prefer a dimmer light. I’ve always preferred viewing the tank under the actinic lights because I really like the blue color and the way that the colors of the corals come out.
Overall, the project turned out as pretty much as expected. Over the next couple of weeks I’ll gradually acclimate the corals to the new light starting with a 2 hour photoperiod and gradually increasing the time the metal halides are on to 6-8 hours. I may also start moving them closer to the surface of the water if I feel the need to increase the intensity of the light.