Re:Thinking about adding a MH pendant, opinions?

Pete Giwojna

Dear Carrie:

As Kris said, metal halides will work fine for seahorses providing that overeating doesn’t become a problem and that you also provide some well-shaded areas for your ponies when they would like to get out of the bright light. ‘Shrooms generally prefer relatively light and most of the other corals you mentioned don’t require high-intensity lighting either, so unless you were planning on adding some SPS corals to your collection, a major upgrade in your lighting system probably isn’t really necessary. A cooling fan will probably be needed to deal with the heat generated by the metal halides and it’s sometimes necessary to add a chiller to the aquarium to keep the water temperature stable in the comfort zone for your seahorses when high-intensity lighting is used.

Here’s the rundown on lighting a seahorse tank with live corals or a reef tank that will house seahorses, Carrie:

Lighting the Seahorse Reef

When it comes to lighting, seahorses do not have any special requirements other than the fact that most species prefer low to moderate light levels rather than excessively bright light. They have a corrugated retina especially rich in rods, which gives them excellent visual acuity under twilight conditions and low light levels in general. But this does not mean that they shun bright light, just that they appreciate shady retreats as well as brightly illuminated areas.

In actual practice, seahorses will do well under any type of lighting you prefer — from metal halides to power compacts or VHO lighting to daylight fluorescent tubes to ambient room light — providing shaded areas are available to them and overheating does not become a problem.

So don’t scratch seahorses off your list of reef-safe fishes just because you keep corals that require bright light. Hippocampus is often displayed under metal halide lighting at public aquaria and zoos (Seahorse Husbandry Manual, 2002), and I know many reef keepers who keep seahorses in their systems under metal halides. Often the reefers will keep the coral and inverts that require strong light at one end of the tank, where the metal halides are concentrated, and keep the other of the tank shaded to accommodate the seahorses, reserved for corals that don’t need high-intensity lamps. Or they will use pendants as spotlights, focusing the metal halides on the areas with corals that require the strongest light, and leave other areas of the reef less brightly illuminated. This can produce a very attractive affect similar to sunbeams filtering through broken clouds. If need be, you can also provide shaded areas by positioning sections of aluminum foil atop your aquarium that are the right size and shape to cast shadows where you want them below.

In fact, my primary concern when using metal halides on a seahorse tank is the water temperature rather than the intensity of the light. Metal halides throw off a lot of heat and most of the subtropical/tropical seahorses do best at temperatures of around 73°F-75°F (23°C-24°C); so avoiding temperature spikes above 80°F (27°C) is very important.

Personally, I like to provide my seahorses with a natural day/night period that includes twilight periods at "sunrise" and "sunset." To accomplish this, I like the power compact (PC) light fixtures that include two tubes — one actinic and one daylight fluorescent — with dual ballasts so that each ballast can be placed on a separate automatic timer. I like to have the bluish actinic come on before the daylight tubes and stay on after the daylights go off, thereby providing a simulated dusk and dawn (Giwojna, unpublished text). This is important for seahorses since they conduct most of their courting and breeding in the early morning hours under twilight conditions. It’s a neat effect and fish and invertebrates can then anticipate "lights out" rather than being plunged into total darkness at night or suddenly thrust into bright light in the morning. I also adjust the timers to lengthen or shorten the daylight periods in accordance with the changing seasons. I find that maintaining a natural cycle this way aids reproduction (Giwojna, unpublished text).

In short, I find PC lighting to be a good compromise for a seahorse system. Power compacts provide plenty of light for macroalgae or the seahorse-safe soft corals in a modified reef system without being too bright or generating too much heat, and the dual ballast system allows for a natural day/night rhythm that changes with the seasons. The resulting dusk and dawn facilitate courtship and help the seahorses maintain a natural reproductive cycle (Giwojna, unpublished text).

For all intents and purposes, you really can’t go wrong no matter what lighting system you chose as long as you provide both shaded areas where your seahorses can escape from the light altogether and well-lit areas where they can bathe in bright light as they please. You will find your seahorses will move into and out of the light often, seeking the comfort level that suits them at the moment.

Best of luck with your lighting upgrade, Carrie!

Happy Trails!
Pete Giwojna

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