96w PC - How Deep will this penetrate

[john0087]

Hey all,

How deep will a 96W PC light penetrate?

Thanks

John

 

[dskidmore]

Light decreases proportionally to the square of the distance from the light source.

What size tank are you putting this on? Are you using one 96 W bulb, or more?

 

[john0087]

I saw a coralife fixture 4x96PC 48" long. I plan on using it over a 75gal reef 48x18x20

So the tank will be 20" tall + 2" legs for the fixture - 3" sand bed = 19" from light to bottom of the tank,

About 17" of water and 2" of air to pass through.


Due to various constraints, I can not get a MH light.

 

[dskidmore]

You could definately keep a large variety of soft corals under that light.

 

[steve-s]

4x96w PC on a 20" tall tank would support a fair amount of corals including LPS and sellect SPS, not just soft corals. Just be mindful of how high above the water the light source sits. The higher it's elevated, the weaker the light penetration will be. Otherwise you'll have few issues at all unless wanting an SPS/clam dominated reef tank.

If upgrading tanks sizes and swapping light dependant inverts you already have, be sure they are placed on the bottom once the new tank is ready. The sudden increase of light intensity will be damaging otherwise.

Cheers
Steve

 

[tecwzrd]

The sudden increase of light intensity will be damaging otherwise.

Steve, are there other alternatives to reducing light damage other then moving all to the bottom? Can filters be used effectively? Could only half the lights be turned on or only all for a couple of hours a day? Is it right that new bulbs have to be broken in also? How long should the corals remain at the bottom and/or lighting reduced/filtered (if possible)

I only ask out of curiosity because I’m still somewhat new to corals and also wonder what someone would do if they didn’t have room to put all their corals on the bottom for whatever reason.

TIA

 

[steve-s]

If upgrading a whole tank at once yes. You can use screen door material as shielding. The brighter the light the more layers to use. After a week or two, start removing one layer a week until it's back to full intensity. This works best with MH fixtures though. It should also be considered when altering kelvin output.

PC's are little easier/forgiving. Sometime altering the photoperiod works, or just running one bulb (½ the bulbs) and slowly increasing the time of the second ½ every few days by ½hr at a time. By far the easiest is elevating the light itself. PC lights can lose quite a bit of their intensity from a simple 3-4" elevation.

When adding new corals, the above are not really good options as you "upset" the routine of the tank. Best they are placed in the bottom of the tank or at least near the substrate. The coral can be adjusted upwards every few days (if PC) until the desired location is reached. Caution on leathers though, they hate being moved. With MH, you will want to extend that time to at least a week before moving a coral upward if at all depending on species.

Cheers
Steve

 

[tecwzrd]

Thanks Steve. Only had one other question. Is screen door material safe to use with MH lighting as well due to the heat the bulbs put off if moving corals wasn’t an option? How high would you have to raise the MH lighting compared to PC if not?

Thanks again

 

[dskidmore]

The metal screening won't melt.

 

[steve-s]

Is screen door material safe to use with MH lighting as well due to the heat the bulbs put off if moving corals wasn’t an option?

As noted above, get the metal type. Just be sure it is not plastic coated as some are sold.

How high would you have to raise the MH lighting compared to PC if not

Depends on the starting height relative to the water line and the intensity of the bulbs. Water clarity will also factor in here. Generally speaking though, for every 3" raised above optimum, you potentially reduce the light penetration by as much as 30%.

Cheers
Steve