Another lighting question

[coopersx]

Lets sayI have 50 gallon tank and a 100 gallon tank. They both use a single 200 watt power compact for lighting. If I were to place a coral 8 " from the light scource ( at the top of the tank)....would the coral receive the same amount of light even though the the tanks are different sizes. I ask because I really want to know if it matters how many watts of light I use per gallon of water if everything is placed 8" from the light scource.
I am unsure if the light must penetrtae to the bottom of the tank to sustain life at the top.
Thanks. Wayne

 

[murph145]

it would make a difference....
lets say your 50 gallon tank is 3' feet long by 18" wide by 24" tall
your 100 is 5' by 18" by 24"
you use a 200 watts PC set up.... the set up on a 50 gallon recheases all areas from front to back side to side in a more complete coverage.... that same set up over a 100 gallon is going to have some empty space because the bulbs are not long enough to cover that long of a tank.... meaning you would need more bulbs positioned to get the same coverage in a tank twice the size....
if u had 200 watts over a 100 and u kept a coral right under it, that might be fine but u couldnt really keep anything where the lights done cover as well lets say the sides....
then if u split the 200 watts up to get a more uniform coverage and put 100 on each side you would have hlaf the wattage on each side and it wouldnt be strong enough but for maybe some low light mushrooms and zoo's
the rule of thumb of watts per gallon although debatable is an easy to use guide line that makes sence and makes it easier to determine if you should have enough lighting over your tank...

 

[tthemadd1]

Well done Murph... You da bomb....

 

[murph145]

tthemadd1 Well done Murph... You da bomb....
Thanks!!! tthemadd1

lighting is hard to figure out at times and doesnt make sence .... but basically the more watts over your tank the more you can keep.... id say if u want to keep a decent reef tank with some softies and some LPS corals i would get a minimum of 4-5 watts per gallon....
when putting that over a 100 that means about 400 to 500 watts.... i learned the hard way and i finally have it set up right with 2-250W MH De 20K and 2x65W 10K PC's over my 100 and it looks great....
heres a small diagram i drew you to show how the light wont cover right and you will have dead spots in your tank wherea coral wouldnt survive.... if u got 200 watts pc u might as well get the 50 to keep corals in that way u can position corals everywhere in the tank

 

[coopersx]

Hi Murph. Thanks for the excellent reply. Sorry took so long getting back. Here is a pic of my setup. A 54 gallon corner tank with 5 week old live rock (cycled in 6 days...I also never got an amonia or nitrite spike after adding fish...only during the live rcok cycle) I do a 3 gallon per week water change, have a bio-ball wet/dry filter with an Aqua C Urchin/Maxijet 1200 in the sump. This tank just finished a 2 week long severe brown diatom bloom. I let it cycle itself out...I thought it would take months. My top off water comes from our well and has 0 nitrate and 0 phosphate...Silicates????? I'll soon find out if this blooms again after a recent 3 gallon water change.
I only have 2- 65 watt power compacts. I am going to upgrade to 2- 65 Blue actinic and a 250 Watt metal Halide in the near future. I got this light (the dual 65 watt PC) to help with the Coraline algae...(whichever type it is that prefers better lighting?) so I did not get the metal halide yet. It is a tough choice for lighting this tank. It is so narrow in the back where the rock begins. I had to go with 24" tubes. I may go with a DYI setup using Ice Cap electronic ballasts.
I have a few invertabrates high up in the tank... and so far so good. All are 2-3 weeks old and still alive. I am suprised the Condylatic Anemone is keeping his footing at the bottom of the tank. I figured he would move towards the top where the lighting is better. Anyway I sure hope he does not move and contact one of the corals. Thanks for the excellent reply. Very well stated. Sincerely, Wayne
Here is a link to my Aquarium Web page:
http://www.wayne-cooper.com/photo_gallery24.htm

 

[murph145]

lookin good....
i think you'll do good with the lighting... would end up doing the MH if i were you .... only thing is the heat.... i had to get a chiller for my tank to keep the temps down once i got my MH's hooked up ....
but it will deffinately make the tank look better and the corals happier....
and by the way your welcome for the reply hope it helped somewhat