Upgrading question

[7digits]

I'm getting a 250w halide fixture on Friday. Right now I have 4 24w T5's. How do I go about getting my tank inhabitants acclimated to the new, brighter light fixture?

[blennydude]

I have heard a number of different methods. You could put 2 pcs of screen under the light, remove one after two days, then the last after another two. You could raise up the light and lower it a couple inches every couple days. Or just turn it on for only two hrs. the first day and raise the time on from there. You might need to adjust height of lower light corals like mushrooms also.

[7digits]

What knid of damage will I cause by just putting the fixture on there and turning it on. I have 2 clowns, a goby and pistol shrimp, cleaner shrimp, some anathelia, some zoas, a galaxea frag, 3 heads of frogspawn, a monti, a few duncans, an stag acropora, a green slimer, and some palys. Tomorrow an enchinata is coming along with a dendro colony and a maxima clam. Also coming is a rainbow monti and a joker acropora. Raising the light is not an option because it sits on top of the tank.

[Ninong]

I'm getting a 250w halide fixture on Friday. Right now I have 4 24w T5's. How do I go about getting my tank inhabitants acclimated to the new, brighter light fixture?

What you're trying to do is gradually change the intensity of light that strikes the corals from what it was under your previous lighting to what it will be under your new lighting. The best way to do that is to use a simple luxmeter to measure the intensity of your present lighting, then adjust your new light fixture so that it registers the same light intensity. You would do that by raising the metal halide lamp to a point where it registers the same light intensity as your present lighting at, let's say, the water's surface.

Obviously that may not be possible. You may not have a luxmeter and you may not be interested in paying $95 for one. Your new metal halide fixture may or may not be capable of being raised. If it is, that's great!

If you don't have a luxmeter, you can simply look at the intensity of the light striking the sand bed in your tank with your old fixture and then position your new metal halide fixture so that it appears to provide equal light intensity on the sand bed. Then, over the next three weeks, you would gradually lower you metal halide fixture just a little bit every few days until you have it in its final position.

It takes a minimum of three weeks for corals in their natural environment to adjust to a new lighting situation. There are several physiological changes that have to take place and those changes take time. That's why it's best to allow at least three weeks for the adjustment. A lot depends on the difference in intensity between the old lighting and the new lighting. The bigger the difference, the longer you should take. If there is very little difference, then you don't have to worry about it much, maybe not at all. This is sort of like the length of time you drag out a slow-drip acclimation of snails or sea stars depending on the difference in salinity between their old water and your aquarium. The bigger the difference, the longer the acclimation period.

If it's not possible to change the position of the new light fixture, then you should consider adding shade cloth of some sort to the top of the tank and then gradually removing it. You could even stack three or four sheets of plastic eggcrate over the top of the tank so that the opening for the light to pass through is really small and then remove one sheet every four or five days.

The least desirable way to acclimate would be to reduce the daily photoperiod. This isn't the best way to do it, so this would be your last resort. This method would have you starting out with just five or six hours a day of metal halide lighting and then gradually building up to your final desired photoperiod of 10-12 hrs/day, or whatever you plan on using for your desired photoperiod.

The best way by far is to start out with the light fixture higher and then gradually lowering it over a period of three weeks.

[Ninong]

What knid of damage will I cause by just putting the fixture on there and turning it on. I have 2 clowns, a goby and pistol shrimp, cleaner shrimp, some anathelia, some zoas, a galaxea frag, 3 heads of frogspawn, a monti, a few duncans, an stag acropora, a green slimer, and some palys. Tomorrow an enchinata is coming along with a dendro colony and a maxima clam. Also coming is a rainbow monti and a joker acropora. Raising the light is not an option because it sits on top of the tank.

What exactly do you mean when you say the light "sits on top of the tank?" You can't have a 250w metal halide lamp sitting on top of your tank. It should be at least 8-10" above the surface of the water. In fact, the manufacturer recommends a minimum of 30cm (12") above the water's surface.

How much water volume do you have in this tank? You are going to get some serious heating of the water with a 250w metal halide lamp if you position it too close to the water's surface. Real serious heating.

Is this a mogul base lamp or a double-ended lamp? Does the fixture have a UV shield?

[Ninong]

I forgot to answer your first question. The damage that you could cause by "just putting the fixture on there and turning it on" is that you could kill or seriously damage your corals and anything else (clams) that contains zooxanthellae. They would bleach (expel their zooxanthellae).

[Ninong]

If the metal halide lamp is a DE (double-ended) 250w lamp and you don't have a UV shield on the bottom of the fixture, you could kill all of your fish within a matter of four or five hours. That has been done and reported online by someone who should have known better because she's a professional marine biologist. It was sort of a confession post. Actually, it wasn't a post on a board, it was a feature article in one of the better hobby magazines. The magazine was Coral and this article appeared several years ago. I have every issue, so I could find it eventually but I would only look for it if someone doubts it.

[7digits]

Thank you Ninong I value your opinions. It is a double ended hqi buld with tempered glass shield. The mounting legs are 3 1/2 inches which would put the fixture after measuring at about 5 inches about the water. It does have a cooling fan. I looked at the coralife and the marineland fixture and they seems to mount the same way but about 3 or 4 inches above the top of the tank. The same as the sunpod. I suppose I will pick up some eggcrate and do it that way. My concern now is the heighth of the fixture.

[Ninong]

It is a double ended hqi buld with tempered glass shield. The mounting legs are 3 1/2 inches which would put the fixture after measuring at about 5 inches about the water

As long as it has a decent 3/16" tempered glass UV shield, I think you should be okay as far as UV radiation is concerned as close as 6" above the water. I wouldn't personally want to go any closer than that but apparently some manufacturers see nothing wrong with it.

The other issues with positioning metal halide lamps close to the water are light spread and water heating. That lamp puts a considerable amount of heat into the water. You will have to watch for that. I'm not familiar with that fixture but I assume the manufacturer has designed the reflector to accomodate having the lamp so close to the water's surface, otherwise you won't get very good light coverage.