210g lighting question

Left C

Lifetime Members
Sep 26, 2005
Burlington, NC
This person bought a 210g tank. It's dimensions of that tank are approximately 72L x 24W x 30H. She wants to make a freshwater planted tank and she didn't do any research. Her LFS didn't know any thing about planted tanks and sold her two saltwater fixtures that have 1 96w Actinic and 1 96w 10,000K in each one. She knows that she has to swap out the Actinic bulbs for plant bulbs.

That will give her 384 watts for her 210g tank or ~ 1.8 wpg of lighting. Is that enough lighting to grow most plants if she adds a pressurized system? The tank is 30" high. Also, what if she decides to not use CO2 , what are her options?

I'm a little confused about the amount of lighting that she needs.

I used two different lighting calculators. When I used the DrHelm.com calculator and I got for lighting, she will need:
~ 450 watts of lighting for plants with low light requirements, (2.1 wpg)
~ 675 watts for Plants with medium light requirements (3.2 wpg) and
~ 900 watts for plants with high light requirements. (4.3 wpg)
Calculate the Water Volume of Your Aquarium

I don't think that this calculator is giving the right answer for a tank of that size. I know that the watts per gallon rule goes out the window with small tanks and large tanks. Small tanks need more wpg and large tanks need less wpg to grow the same plants.

Then I used another calculator that is based on a study of Amano's tanks, I got a much lower light light level. I got ~ 265 watts (1.3 wpg). That's a big difference between the two calculators. Lighting in Amano Aquaria

Some people like to use MH or HQI bulbs to penetrate down deep into the water for tall tanks like she has but she doesn't want to use MH or HQI bulbs..

I asked her this question too. Here's something else to consider about your 30" tall tank. Are you going to be able to plant it, trim the plants and do the maintenance in it?

Is her present 1.8 wpg OK w/o CO2 or does she need CO2?
Does she need to add another 384 watts of lighting for 3.6 wpg and CO2?

Thanks in advance!

Greg Watson

Staff member
Jan 23, 2005
United States
Left C;15884 said:
Is her present 1.8 wpg OK w/o CO2 or does she need CO2?
Does she need to add another 384 watts of lighting for 3.6 wpg and CO2?

Thanks in advance!

There are many different answers to your questions as there are people. 10 years ago, we thought anyone with 1 watt per gallon of light was crazy. Today, 1-2 watts is normal and 2-3+ is very common ...

Does she need CO2 at 1.8 wpg? Yes ...

Does she need more light? That is a function of how fast she wants her plant growth to be forced ... personally I really like and prefer tanks in the 1.5-2.5 range, in my opinion, they are easier to maintain - yet still have excellent plant growth rates ...

Now that said ... there are lots of legitimate reasons to make an argument for less light as well as legitimate reasons to argue for higher light ...

There are a few plants that need higher lights ... so if there are specific plants that require high light that she absolutely has to have ... then that would be a legitimate argument for higher light ...

But in general ... she is just fine ...

I have a 180 gallon tank that I normally run at about 2.3 watts per gallon ... but when things get hectic, one of my standard routines is to simply unplug one of the banks of lights and drop it down to about 1.5 watts per gallon ... that quick change reduces a lot of my *problems* ... for example, I've been finishing up graduate school and for the last year, I've reduced the lighting level down to about 1.5 watts per gallon because I just have not had the time to provide the kind of daily maintenance that I am accustomed to ... and slowing down the growth rate made it a lot easier to maintain ...