Metal Hallide Hight Above Tank?

[newbeemike]

I have a 75 gallon SPS tank. With a sunpod 2X250 48" metal hallide fixture. I originally had the light sitting directly on the tank (with the provided legs). I have noticed that no matter how deep I put my coral I keep bleaching them. I have even bleached some of my rock. My water specs are perfect, so I assumed that it was a light "overkill". I just mounted the light 6-7 inches over the tank using a hanging ceiling mount. Is this a good height? what height to you recommend?

[Bifferwine]

I'd recommend starting about 18 inches above the water, and gradually moving it down. My lights are hanging about 18 inches off the surface, and I've not had any problems with bleaching, but I have had problems with them overheating the tank.

[ccCapt]

2x250 mh over a 75 is alot, but not enough that it alone would cause bleaching. Are all SPS's bleaching, or only certain types? What kind (brand, K temp) of bulbs are in there now and when was the last time you changed them.
Can you list your "perfect" water parameters? Specifically salinity, pH (after the lights have been on a few hrs), nitrate, calcium, alkalinity, magnesium and phosphate?
What salt do you use? Do you dose anything and if so how often?

[newbeemike]

Salinity= 1.022, Calcium =500, Nitrate= 0, PH (dkh 12), phospate=0, Have not tested magnesium. temp is 79. I do weekly water changes of about 10 gallons. Top off with RO water system I have installed at my house.
I ususally don't mix the salt myself. I get salt water weekly from my lps. He says the water is great. He uses it in his SPS tank with no problems. Lights are 14k. Original bulbs. Unit and bulbs are only about 6 months old

Originally Posted by ccCapt

2x250 mh over a 75 is alot, but not enough that it alone would cause bleaching. Are all SPS's bleaching, or only certain types? What kind (brand, K temp) of bulbs are in there now and when was the last time you changed them.
Can you list your "perfect" water parameters? Specifically salinity, pH (after the lights have been on a few hrs), nitrate, calcium, alkalinity, magnesium and phosphate?
What salt do you use? Do you dose anything and if so how often?

[newbeemike]

dose oceans blend daily, Started using purple up again. Seeing how rocks bleached. I had no problems with my rocks before I put the metal hallides on. they were covered with purple coraline algea which all died after putting lights.

Originally Posted by Bifferwine

I'd recommend starting about 18 inches above the water, and gradually moving it down. My lights are hanging about 18 inches off the surface, and I've not had any problems with bleaching, but I have had problems with them overheating the tank.

[newbeemike]

Salinity= 1.022, Calcium =500, Nitrate= 0, PH (dkh 12), phospate=0, Have not tested magnesium. temp is 79. I do weekly water changes of about 10 gallons. Top off with RO water system I have installed at my house.
I ususally don't mix the salt myself. I get salt water weekly from my lps. He says the water is great. He uses it in his SPS tank with no problems. Lights are 14k. Original bulbs. Unit and bulbs are only about 6 months old

[ccCapt]

Reef Aquarium Water Parameters by Randy Holmes-Farley
You salinity is low for coral. Should be 35ppt or 1.026.
Calcium is too high. Should be around 400. Having it higher won't hurt anything, but it does no good either.
pH and dKH are 2 different things. dKH is alkalinity and 12 is on the high side.
You really shouldtest your mag.
Why are you dosing PurpleUp? That's calcium and your ca is too high already.
What exactly is Ocean Blend? What's in it?
What test kit are you using that reads 0 ppm for phosphate?

Did you light acclimate everything when you installed the new lights? Like maybe only on 2 hrs of full balst mh at first and gradually increase the duration?

[JAG107]

light doesn't bleach coralline, at least not that i know of.
Ccapts right, test your mag, slowly raise your salinity to at least 1.025
Phos should be tested with at least a salifert kit, or a more expensive (ie better) one than that. API or other cheap kits all read zero unless you're toxic with them (1ppm or more)

[daugherty]

yes to much light will bleach coraline.

[Oscarsdad608]

It does sound like bleaching to me, but your salt level is low too. I would hang the lights like you planned. If you can cover the tank in window screening. Place about 4 to 6 layers and remove 1 about once a week or so. In the higher spots in my tank the coraline is alot lighter.