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Discussion Starter · #1 ·
Hi all,
I just got a new 90g and am running a fishneedit 4x39w 36" light in the front of my tank and the 48" 2x54w fixture that came with my fluval frontier, so a total of 264w divided by 90 is 2.9wpg. Would it be reasonable to add 25% to that figure since it is t5 lighting? I do want to grow high light plants and am going to run co2. Do I have enough light to grow pretty much anything?
 

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WPG is an outdated and inaccurate measure. It doesn't take into account: distance away from the tank, reflector quality, type of light, etc. I would advise you to stop using it. If I told you that I had 50 wpg but I hung my light 1 mile above my tank, do you think I'm getting good light to the tank?

Let us know some details about how far above your tank the lights are, how high your tank is, what kind of bulbs they are (you said T5, I'll assume all are T5HO), etc, as well as what kind of reflectors you have, and a lot of people here can tell you more about your lighting.
 

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Discussion Starter · #3 ·
yes I realize it is not the best way to measure, but I do not know of any other ball park rule of thumb for estimating lighting. The lights are T5HO. T5 is supposed to be 25% brighter per watt. Anyway, the tank is 48 wide 18 deep 22 tall. i have a background in the tank that takes up a few inches in the back so I have the lights jammed towards the front of the tank
 

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That is a crap load of light. Part of why WPG fails is because of difference in efficiencies in bulbs, reflectors, etc. The other part is on small tank and big tanks, the rules aren't the same. It is more about distance from bulb to substrate. And since on a 90g tank it isn't as if it is 3x as high as a 29g tank, you only need enough to spread it out.

YOu could easily do fine with half that much, depending on reflectors and spread.

What I can tell you is that using that much light, you will be chasing it with co2 and ferts, rather than using light as the control. What this means is that WHEN(not if) algae comes, you'll be playing catch up and always playing with the wrong kind of green stuff.
 

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Are you sure it's 22 tall? A standard 90G is 48x18x24. a 75G is 48x18x21. You have enough light to grow pretty much anything with just the 2x54W fixture, but since a 90G is so wide, it's hard to spread the light from front to back well. However, if your tank is only 75G, you already should have enough light with just the 2x54W fixture, as that tank is 3 inches shorter so the lights are closer. I'm assuming you don't hang your lights so that they are pretty much right on the tank. You are most likely already overdoing the light by a lot.
 

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at only 22 inches tall that is LOT of light. A Lot. Like way more than you could need.

BTW, it sounds like those measurements are much closer to standard 75g tank, not 90.

90g that is 48x18 would need to be 24 or 25 inches tall.
 

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Discussion Starter · #8 ·
Are you sure it's 22 tall? A standard 90G is 48x18x24. a 75G is 48x18x21. You have enough light to grow pretty much anything with just the 2x54W fixture, but since a 90G is so wide, it's hard to spread the light from front to back well. However, if your tank is only 75G, you already should have enough light with just the 2x54W fixture, as that tank is 3 inches shorter so the lights are closer. I'm assuming you don't hang your lights so that they are pretty much right on the tank. You are most likely already overdoing the light by a lot.
oops youre right it is 25" from bottom to top,
 

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Discussion Starter · #9 ·
at only 22 inches tall that is LOT of light. A Lot. Like way more than you could need.

BTW, it sounds like those measurements are much closer to standard 75g tank, not 90.

90g that is 48x18 would need to be 24 or 25 inches tall.
What I have been doing is running an 8 hr photoperiod for the 4x39w 36" fixture in the front, and a 4 hour mid day with the 2x54w... Too much light?
 

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Discussion Starter · #11 ·
wow that chart at the bottom is helpful. So it seems like I could get by with just the 36" fixture if I wanted to. I am amazed how much the reflectors matter! The 36" fixture is from fishneedit.com, each light has individual reflectors. It looks high quality. The 48" has one reflector. I have the option to turn off 2 of those 36" lights too, maybe I should do that?
 

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Discussion Starter · #13 ·
Wow Hoppy, I hadn't checked the sticky for a month or two now, and looked what popped in there... more graphs! Super nice! OP, you can see why WPG means nothing because it doesn't tell us about a lot of important factors.
Yes I knew it was inaccurate but I didn't know it was quite that bad.
Can anyone offer any suggestions for the lighting schedule and intenity now that you know what I am working with?
 
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