melev

The metal halide bulbs are key to growing corals in my reef. Day after day, the bulbs light up the display and the corals grow. Over time, the bulbs weaken and even shift spectrums, which can result in unpleasant pinks or yellows that make the corals appear ugly... and even worse: algae will grow. The easiest cure is to replace the bulbs. I've been dragging my feet on this project out of sheer stubbornness. I really wanted to change them out when the 400g was back. That's when I have to take the entire light rack down, move it over the 400g and reinstall all the reflectors, ballasts, and cords.

But while the corals are doing well, the look of the tank was bugging me. Turning a blind eye to the shift in color spectrum wasn't working as well as you'd think, and I found myself trying to will myself to hold out. A few days ago, I was looking for something and came across my bulb stash and my resolve began to weaken. Everything else is being maintained so why was I holding out on changing the light bulbs?

I have new bulbs and some used ones. The used ones can be useful if you need to test a ballast or if someone in the area needs an emergency bulb until a replacement can be purchased. Going through the new bulbs, I had three ReefBrite Twin Arc bulbs that I'd never tested. I got them right after I'd installed new bulbs over my tank some time ago, and were set aside until a better time. Like now.

Below is a comparison of a standard mogul Metal Halide bulb, in this case an XM bulb. Above that is the ReefBrite Twin Arc bulb. You can see how there is one pillow in the bottom bulb and two pillows in the upper bulb. That pillow is the actual light source, and each one provides a separate spectrum when powered up. They will never be lit at the same time. You can purchase Twin Arcs with the same spectrum if you prefer, with the idea that it will last twice as long before needing to be changed. The bulbs I'm using are 10,000K & 20,000K. Running 10,000K during the daytime provides a good spectrum for growth, and running 20,000K provides the nice blue that makes corals pop with color -- to be enjoyed in the evening for example. Your schedule may be nicer with blue first thing, and then white while you leave for work... that's up to you.

After all these years, my Lumenbright reflectors still look picture perfect which I attribute to the glass pane and regular cleaning. The twin arc is installed, and the used 400w XM bulb is resting on the surface of the glass pane for comparison.

When changing Metal Halide bulbs, never handle them with your bare hands. A tube sock is a great way to unscrew and screw in a new bulb. If you are using double-ended bulbs, slide the sock over your hand like a sock puppet for the exact same premise.

I was excited to see what the tank would look like when the bulbs were on. The default or first arc to light was the 20,000K spectrum.

Using the Apex App, I turned off all three bulbs and turned them all on again about 10 seconds later. Within a minute or two, the 10,000K arcs lit up.

When changing out the bulbs, especially really old ones like mine, it's best to get a PAR measurement of the light as it is now, and then again after the new bulbs are installed. With those numbers, you can see why it is important to change the duration of the light cycle to a shorter period to avoid burning the corals.

These measurements were all taken with the probe right at the surface, directly under the center of the bulb. The top row is the old bulbs I just took out. The second row of numbers was with the 20,000K lighting, and then the third row were taken after toggling the bulbs off and on to get 10,000K lighting. Remember that old bulbs are way over a year old. I'm not comparing these numbers as a negative about the previous brand but to avoid bleaching corals with brand new bulbs.

Look at the difference from the middle 400w bulb, from 20,000K to 20,000K! 633 to 1321. That's more than double the intensity. Yes, I'd have to run these lights less than their regular six hours a day. And if I switch to the whiter 10,000K spectrum, it is nearly 300% more intense (and not as pretty although that's what corals actually look like in direct sunlight).

The outer bulbs are 250w each, and the old 10,000K compared to the new 20,000K arc provided very little difference PAR-wise. However, when you compare them 10,000K to 10,000K, the outer bulbs are about one-third more intense (560 to 880 and 640 to 940). Again, running the lights for a shorter timespan is a must, and I can ramp up the lighting period over a couple of weeks to let the corals adjust to the increased PAR.

Finally, I also moved the PAR sensor around at the surface to see how the numbers change. Because of the faceted Lumenbright reflector, there were areas that measured less and other areas that were even stronger. The 10,000K bulb measured 880 in the center, but moving the sensor about 6" closer to the front of the tank provided a reading of 1100 PAR. The arc section of the bulb can't be dead center in the reflector because there are two, so the mirroring effect puts the hot spot in a different area than one might imagine. Owning a PAR meter really is useful even if it isn't used often. It allows me to check placement of livestock and prevent damaging those corals when changing bulbs.

It's only been a few hours since I fired up the Twin Arcs but so far, these are pretty cool.