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Discussion Starter · #1 ·
Hello everybody,

I am in the process of setting up a 75 gallon planted FW tank (48x18x21). Initially, I will try to run the tank without CO2 fertilization. I am going to build the stand and the canopy myself. For the canopy, I plan to order the AHS PC lights, but I am not sure which ones:

First of all, on the AHS site, they claim the efficiency is about 65% higher than other reflectors with the same bulb. If I try to target 2 - 2.5 wpg, that would suggest that I only need 1.2-1.5 wpg, i.e. 90-115W. In addition, 2 wpg with NO FL used to be considered medium to high, and the PC bulbs deliver a much higher output with the same wattage. That would mean that 2x55W would be OK (decent but slowly growing plants), 4x36W would more than enough (faster growing plants), and for 2x96W I would definitely need CO2. Am I correct or completely wrong?

Assuming that I would go with the 2x55W, one of the issues I read about the AHS PC lights seems to be that they are very narrow and focused. Moving them away from the water surface would probably increase the spread. Where is the optimum between loss of efficiency (due to the distance) from the water and spreading the light? Has anybody experimented with that? It sounds from some of the posts that bending the reflectors would increase the spread. How does impact the efficiency?

Thanks for your help,
Frank
 

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I would go with four 55 watt bright kits for a 75. Thats what I plan for mine when I can afford it. You could probably adjust the ammount of light the tank recieves by raising the bulbs further above the surface untill you get what you like. You could even suspend them above the tank and have an open top tank! Then, if you ever do decide to use co2, all you would have to do is lower them back down.
 

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If you want to run the tank without CO2, then I'd say you need to stick to 2WPG and under. In which case, two 55w bulbs would be sufficient but not a very good spread. About the reflectors, sure they reflect light in a narrow beam, but they are not magical. If you focus light in a narrow beam of course you get many times the intensity in a single spot than if the light was spread out more, any reflector will do this, just bend it to your liking, but unless you are covering most of your surface area with such narrow light, the spread will be a little too narrow for you IMO. What I'm trying to say is don't think you will need less w/gal because you are getting the AH Supply reflector, it just reflects a narrower beam, good penetration but poor spread, amount of light remains the same!

I'd consider T8 tubes seeing they can cover the surface area far better than what CFs can for the same amount of light. Three 32W T8s would be better in my opinion than 2 55W CFs. They will also give you the possibility to mix different bulbs together. All-Glass also sells a tripple T8 fixture that would be perfect for your tank, comes with the popular Aqua Rays bulbs too. I paid $99 for mine at Pets Plus, I use it on my 90 gallon. If you have a canopy then you can even space the bulbs out further to increase the spread more.

Hope that helps
Giancarlo Podio
 

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Discussion Starter · #4 ·
Thanks for the comments so far!

I think what I am realizing at this point is that - going with PC - I will have to use two PC bulbs side by side to get the spread. Also, I should try to stay under 2wpg. Even if I add CO2 later, I do not want the plants to grow too fast (I do not want to spend more time cutting the plants back than watching the tank :) ).

So right now, I am leaning towards 4x36W or maybe 2x36W(background)/1x96W(foreground), which gets me to around 150W for the whole tank. In addition, I can mix 5500K and 6700K bulbs, which seems to be what a lot of people in this forum like and recommend. Since the 36W kits are only about 17", there will be 3.5" on each side and 7" in the middle of the tank uncovered. But I do not expect that to be problem, because the center brace would take away 2 inches from the middle anyway and there should be enough spread.

Regards,
Frank
 
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