The Right Mounting Height for LEDS!

[Rookums Reef]

I've read a ton of posts, found the manufacturers specs and I still have no clue on the height for these Black Box leds I have. The specs say 6" above the tank due to the optic lenses, at 90 degrees. Original owner had them at almost 20" above the tank and lost a ton of corals. The tank is a 40B. I originally got it in August of 16'. Since then the tank has done well but I'm getting different types of algae constantly. All my parameters are normal, I know the tank cycled when I got it back up and running. Have 3 BTA'S, 1 Carpet anemone, hammer, candy cane, star polyps, nice zoas and palys. I dose coral snow and some phyto randomly. Maybe it's not the lights? I'm just tired of cleaning the tank and dosing Chemiclean when the algae gets really bad. I have a 90 RR I'm wanting to transfer to but I need to figure out what is the issue. Any help is greatly appreciated!

 

[mcarroll]

90º lenses make the math for "ideal placement" easy.

Mounting heigh = coverage radius.
Radius * 2 = Maximum Coverage

You can also add the radius to the outside dimensions of the fixture to get the total coverage area. If the light fixture has a 90º lenses, a 5" x 30" footprint, and it's suspended 6" over the tank, then you get a maximum coverage of 17" x 42".
(6+5+6=17; 6+30+6=42)

Worth noting that "ideal" is rarely perfect. It does make a good starting point though.

For example, lenses do not spread light evenly, and the spread/placement of their emitters on shoebox-type fixtures seems to exaggerate this compared to other designs. The effect is usually a very bright middle and a weak perimeter.

Be prepared to experiment!

And if you don't have a light meter of some kind, get one. Anything is better than nothing. Free lux meters for your smartphone are a great starter option, but they can be finicky. Much better to spend $10-$20 on a handheld (my LX-1010B, for example). Of course if you can buy or borrow a PAR meter, that works too!

 

[Rookums Reef]

PAR meter would be great, I'm in a rural area and don't have access to one! That math makes my head hurt, but it works. I just raised the lights, my hanging kit was missing a piece which made me not wanna monkey with it. Now I can move them easier. Just raised them to 20" above and will work my way from there. I guess I figured that only running the lights at 45% blues and 20%whites was gonna be fine to start with? Of course I'm used to another setup and will have to find the happy medium for this tank. Gonna call Hobby Bug and find out how old these are for **** and giggles. Thanks for the info mcarroll!

 

[mcarroll]

What are the dimensions your fixture?

At 20" above the tank, your intensity at 100% will still be about 2-3x dimmer than the default mounting height.