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I'm going to upgrade my lighting on my 75g because I really want to have a better planted aquarium with some harder plants and carpeting. It is a standard 75. So my question is should I buy 1 or 2, 48 in" 3.0 lights? 

Information says that the high lighting requires Co2. I don't know how to set those up. It'll have to be another topic later! 

All input for the lights is welcome. Although best from very knowledgeable planted tank keepers w/o Co2. I'm new to keeping high requirement plants! 

Thank you Sandy 

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Just now, lefty o said:

i would wager that 1 light will do the job. no sense in buying 2, as if you are not happy with 1 you can always add another later.

Thank you , I'm not necessarily stuck on fluval either. It can be a different brand. I just want to make sure I buy the right light for what I want my plants to do. They're so expensive and I'd like to get it right the first time. 

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Hi @Sandy

It really depends upon the plants that you want to grow.  I have a 75 gallon with a Fluval 3.0 on it.  At full output it can provide about PAR@75 at the substrate level (2" - 3" substrate) throughout the tank (slightly higher directly under the fixture).  I was surprised how evenly distributed the light was, wuth most LED fixtures light intensity drops substantially as you move from directly under the fixture. Readings were taken with an Apogee MQ-510 PAR meter calibrated within the last 12 months.  PAR@75 would be equivalent to "medium" to "medium high" light levels. One fixture should be sufficient until you decide to add CO2 to your tank.  Hope this helps!  -Roy

75 gallon with Fluval 3.0 fixture

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41 minutes ago, Sandy said:

Thank you Roy. So if I wanted to go brighter I would need Co2? 

Hi @SandyBasically that is correct.  Plants need nutrients nitrogen, potassium, phosphorus, iron, calcium, magnesium, and several micro-nutrients but they also need carbon molecules for the Calvin Cycle in photosynthesis.  Because there is carbon dioxide in the air a small amount is available in the tank through the gas exchange at the surface but when I increase my light level the plants need more nutrients including carbon molecules - otherwise I end up with an algae farm.  It's all about balance. -Roy

Edited by Seattle_Aquarist
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