Watts per gallon?

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bromie88

Feeder Fish
MFK Member
Feb 19, 2008
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as a rule of thumb, the watts per gallon rule isnt a very accurate way to calculate the amount of light needed for a SW tank. a 30 gal tank can be 30"Lx12"x18" and would need around 90w to reach 3 watts per gallon. a 30 could also be 18"Lx12"x30" so 90w would obviously not be enough, even though it technically is according to the rule.

is there a better way to work out how much light i would need to keep low light loving corals. maybe like watts per inch of depth? would it be possible to keep corals with less watts, just higher in the aquarium? like just under the surface with 50w, or halfway down with 70w?

im asking as i keep finding corals on my rock. the lfs near me that deals with marines is shut for some reason, and i know no one else who keeps marine fish. i couldnt really even take the corals to another lfs, as i wouldnt have much rock left.

i would get more light, but as much as it kills me to say, my tank comes 2nd, as i need a house to keep it in at the end of the day. so i cant really spend too much. i could possibly stretch to another 25w unit. and i have a spare 9w arcpod light i could bolt to the hood. that would give me 84w in a 1ft section of the tank containing the corals and 75w everywhere else. is this enough light to get me started? especially if the corals are as close as possible to the lightsource. 1" in places.

i run 50w of florecent. 25w marine white (10000k i think) and 25w actinic. i would run another marine white. on the other unit. would get higher wattage lights, but the longest light i can have is 30". and 25w are the norm in a 30" lenth.

and i dont have the money to just go out and buy anything else, otherwise i would... my tank would have at least 100w if i did... even though it is supposed to be a FOWLR.
 
that rule of thumb is junk, i agree. A t-5 system without individual reflectors will be fine for low light corals. If this were going on my tank, i would however, try and get individual reflectors. even for a low light coral, the amount of output from 2 t-5 HO bulbs with individual reflectors will make a huge impact on your tank, and your coral, low to medium light will love them. Power compacts are a bit trickier, I'm not a fan of them, they burn there spectrum way to fast and I've never noticed any decent growth in corals. i had 196 watts on a 40 breed, which according to the rule and science behind the light, should have been plenty. its just personal experience but thats not saying you will not have luck. On your size tank, they make a light that would fit it perfectly. For the T-5 they don't actually make a 30inch HO bulb. They make normal powered bulbs but just not the V-HO's or HO's.

hope this wasn't to much rambling for you but lights are weird in every application. Good luck.
 
sweeTang21;2452436; said:
that rule of thumb is junk, i agree. A t-5 system without individual reflectors will be fine for low light corals. If this were going on my tank, i would however, try and get individual reflectors. even for a low light coral, the amount of output from 2 t-5 HO bulbs with individual reflectors will make a huge impact on your tank, and your coral, low to medium light will love them. Power compacts are a bit trickier, I'm not a fan of them, they burn there spectrum way to fast and I've never noticed any decent growth in corals. i had 196 watts on a 40 breed, which according to the rule and science behind the light, should have been plenty. its just personal experience but thats not saying you will not have luck. On your size tank, they make a light that would fit it perfectly. For the T-5 they don't actually make a 30inch HO bulb. They make normal powered bulbs but just not the V-HO's or HO's.

hope this wasn't to much rambling for you but lights are weird in every application. Good luck.
Click to expand...

I agree. I have played with several combo's as well, some well under the accepted "rule of thumb" resulting in both accelerated growth in some species and a decline in others. I have also gone way above and beyond such guidelines and have dealt with the same results (some flourishing, others showing a slower growth rate, or actual burns to tissues). A lot of people get so wrapped up in the amount of watts they need, that they fail to take in the rest of the picture. While yes, watts are important and determine the strength of your lighting; the combination of lighting you use is just as important if not more so, especially when dealing with marine environments and species as their requirements far exceed those of most freshwater animals.
You have to understand the light spectrum, and know what is required of what you are housing in order to ensure health and vitality to your animals. In the ocean, most common retail marine fish and inverts live at varying depts - even those of the same species, and as we know, the deeper you go, the more colors of light is filtered out, and as a result, you get more of the blue - which is the deepest penetrating. Closer to the surface, reds are stronger, and so on and so on. You have to match your lighting spectrum with the needs of the animals, and then determine how many watts are needed for the depth and width of your tank so that light penetrates evenly. It's a confusing science and one which many people fail to truly understand and therefore they simply rely on watts.. But here is something to make it a little more simple... Would you use a 120w incandescent light on your tank simply because it reached the wattage required for it? No, because that would not provide the right spectrum of lighting that the animals required. They go hand in hand, so remember that while descerning such. Watt is important, but spectrum is the other half of a sucessful equation.
 
it's the same way as the inch per gallon rule.. great for noobs to remember.. not so great in technical applications
 
thanks all. all the corals now seem to be looking happier than when i found them. ive moved as many as i could to the upper areas of the tank. some of the ones i thought would be dead when i found them (they where bleached white), are starting to get a bit of colour. they havent opened yet, but i think they may be more mushrooms. everything looks so much better than they did originally, so its looking promising so far.

there is another small (now 5mm across) mushroom near the bottom of the tank that has literally doubled in size in the past few days, so i must be doing something right... which makes a change.:)

and one polyp has opened fully!!! it looks like this. id take a pic but i only have my phone, so quallity is crap.

http://image36.webshots.com/36/8/36/93/2945836930089596439vFKxQO_ph.jpg

thanks again for the help.
 
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