# [Wet Thumb Forum]-couple of questions about lighting



## MarkH (Feb 6, 2003)

Currently I have a 75 gallon tank. It has just 2 regular strips on it for lighting. Since i recently purchased a home my plan is to now buy a larger tank 180-240 gallons. I have never had much success with planted tanks and want to get it right, what I really want is a fixture for my 75 gallon that I can bring up as half of the fixture for the new tank.

I see power compact fixtures that are 48" in length with 4 bulbs ranging in wattage from 55 to 96. I have been trying to research this information but I can only come to the result of 1-3 watts per gallon which would mean about 225 watts for the 75 gallon tank for optimal lighting but a whopping 720 watts for a 240 gallon tank. To me this sounds excessive...I am willing to get it but I would hate to buy too much light for the system. Thanks ahead of time.


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## MarkH (Feb 6, 2003)

Currently I have a 75 gallon tank. It has just 2 regular strips on it for lighting. Since i recently purchased a home my plan is to now buy a larger tank 180-240 gallons. I have never had much success with planted tanks and want to get it right, what I really want is a fixture for my 75 gallon that I can bring up as half of the fixture for the new tank.

I see power compact fixtures that are 48" in length with 4 bulbs ranging in wattage from 55 to 96. I have been trying to research this information but I can only come to the result of 1-3 watts per gallon which would mean about 225 watts for the 75 gallon tank for optimal lighting but a whopping 720 watts for a 240 gallon tank. To me this sounds excessive...I am willing to get it but I would hate to buy too much light for the system. Thanks ahead of time.


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## Doomer (Feb 2, 2003)

I decide to start out with 500 watts of MH lighting (2 x 250 watt fixtures). I may end up needing to add 2 more but won't know until the algae war comes to an end.









My advise would be to keep your options open as to control. Individual fixtures are better than one or two that all have to be on. What I mean is, in my case, having a fixture on each side forces me to run at 500 watts. If I turn one off then half of the tank goes dark. If I end up adding 2 more fixtures I'll have a choice between either 500 watts or 1000 watts lighting the tank more od less evenly.

Hope this made sense.


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## Rex Grigg (Jan 22, 2004)

On small tanks (under 15 gallons) and very large tanks (over about 90 gallons) the watt per gallon rule breaks down pretty quick. If you can get 2 watts per gallon over a 240 gallon tank you will be fine. I would suggest a couple of 250 watt MH lights if you are getting the 240 that's 48" long. The general rule with MH lights is one light fixture for every two feet of tank length.

Semper Fi


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## MarkH (Feb 6, 2003)

let me clarify a little.

My plan is to use my 75 gallon tank which is 48" long to "learn" how to keep plants alive, it just so happens that my 75 gallon tank is half as long as the 240 which is 96" long. What i want is something that I can use on the 75 during this learning process then transfer to half of the 240's lighting. meaning if i got a 48" PC fixture i would buy another one thats exactly the same for the other half of the 240. SO basically how much wattage and what type of fixture can i use on the 75 that could also work well as half of the 240s light? Does this make a lot of sense or does it seem unreasonable?


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## Rex Grigg (Jan 22, 2004)

> quote:
> 
> Originally posted by MarkH:
> let me clarify a little.
> ...


 Well it would work. Best thing to do would be to get a 220 watt fixture from Aqua Botanic. Robert just got in some awesome lights. This fixture would give you just under 3 watts per gallon which will grow most plants and is not so high powered as to cause you much grief. You will need a CO2 injection system though. With that light and a 75 gallon tank DIY is not likely to cut it. You will want to read the Fertilizer Help thread in the Aquarium Plants forum. And that light can just be moved to your larger tank.

Semper Fi


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## MarkH (Feb 6, 2003)

thanks a lot!

I don't see where the light fixtures are listed on the site for sale, am i missing something?


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## Rex Grigg (Jan 22, 2004)

Robert has not gotten them on the website yet. Call him and bug him about the lights.

Semper Fi


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## Heady (Mar 4, 2003)

Is there a better measure for large tanks than watts per gallon?

I'm getting a 60" x 18" x 20" tall 100 gallon tank and find it hard to believe I will need much more light per square foot than my 48" x 13" x 18" tall 55 gallon. 

I am hoping for some kind of watts per tank height or watts per water surface area or something.

This tank will be acrylic, so I'm not sure if the PC flurorescents would be OK since I'm told they run hot.


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## ekim (Jan 31, 2004)

surface area in square inches, multiplied by the distance from the light source 
to the substrate. Then multiply this by 
0.08 for low light plants, 
0.12 for low to medium light plants, 
0.18 for medium to high light plants or 
0.27 for high light plants. 
This will give you the watt hours of fluorescent lighting that you need. Then take this number and divide by 11 and you will have the approximate watt hours of light you need.


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## jpmtotoro (Feb 13, 2003)

ekim, that thing needs to be posted somewhere, screw the wpg thing, i like that one!!! according to it, i'm about perfect for medium light plants which is where i was aiming for. looks like i guessed right. thanks!

JP


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## JamesHoftiezer (Feb 2, 2003)

My tank has 6sqft(864 sqin) and 25in of depth(~22 to substrate).
with 3.3wpg I am getting awesome growth and results including 4-6in from most plants per week. 
Due to the resulting maintenenace, I plan to scale back to 2.2wpg in the future.

I really like the look of the Robert's new fixtures, but I'm not sure how easy it would be to put them end to end across the larger aquarium.

My suggestion would be MH. You could use pendants if you plan an open top or do a DIY hood that you can transfer later and build a twin for it at the time.

*James Hoftiezer

Tank Journal - Aquascape ( Latest / Archive )
Tank Journal - Parts and Construction ( Latest / Archive )*


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