how much light for a 10 gallon tank?

[aquanoob]

After keeping fish for a couple of months we(my wife and I) decided to try out adding some plants to the tank. Our tentative plan is to start with Java Moss and Water Sprite, which (according to plantgeek.net anyway) will grow all right with gravel substrate and are in the low and medium-low light ranges respectively.

My main question is about lighting, specifically how much these plants need. Right now we have a 15 watt florescent light that came with the hood. The guy at my local pet shop suggested replacing that with a 15 watt bulb designed for planted tanks. From what I've read here 1.5 wpg is probably enough for a larger tank... but I'm not sure about a 10 gallon. Is what this guy told me sane or do I need more light? If so how much?

Also:
CO2 seems like a lot of trouble (and expense) Is this something that is really necessary for these plants?

Do I need to add anything (besides fish food) to make these things grow?

Is there something that I should be asking that I'm not?

 

[jrp1588]

I rigged up a CO2 thing for just the price of a soda bottle, some yeast, some sugar, and a little tubing. Dunno how much actually gets absorbed because I don't have a reactor thing. I didn't understand the DIY instructions on that one.

 

[greenmaji]

small tanks are debateable.. there is a minimum light threshold theory out there(LOL rex griggs..LOL) that says that the normal wpg rules dont apply ie you need alot more light to grow plants in small tanks.. this is how I see it.. you have fairly non demanding plants.. as long as you have a bulb that has good color temperature I would just try to use it (if you want to make sure the color temperature is in the right range.. look at the color light its making.. if its red-orange.. its likely too low.. and the florescent lighting isle of any department or hardware store has daylight bulbs that are in the correct range..around 6500K and 5000K) if the plants seem to not do well with the 1.5wpg your giving them after a while you can always alter or upgrade the lighting.. HTH

 

[jrp1588]

Why do smaller tanks need higher wattage? I'd think they'd need less if anything. I don't get it.

 

[aquanoob]

Why do smaller tanks need higher wattage? I'd think they'd need less if anything. I don't get it.

my understanding... WPG is a measure of light(indirectly) per unit of volume, but what actually matters is light per unit of area. since volume is proportional to area^(3/2) not area^1 the WPG rule breaks down at either extreme of the volume range.

 

[greenmaji]

the argument goes something like this.. its the lumens that make contact with the surfase of the tank per square inch.. the smaller bulbs dont put out the same lumens per inch as the bigger ones if I understand the argument corrcetly.. and since the lumens or total light ouput is what really counts then you would need more lumens to do the same job for the little tank.. its a heady argument and I think you can experiment with your light untill you get good results intead of worrying about it.. unless of course your wanting a high light high tech little tank from the get go.. then I would say get more light then normanl.. like 4-5wpg just to be on the safe side.. HTH.. you could read the argument on this link..
http://www.rexgrigg.com/mlt.htm

 

[jrp1588]

So why not just measure it in watts per square inches of surface area? Seems like that would give a much more uniform measurment if I understood your statement correctly.

 

[greenmaji]

it would be lumens per square inch.. and that would be hard to understand for most people...

 

[jrp1588]

What exactly is a lumen? How does one determine how many lumens they have? My physics teachers skipped this chapter I suppose.

 

[greenmaji]

lumen is a measure of light intensity by.. 1 lumen is what 1 candle would put out from one foot on one square foot of surface. and the average 4 foot NO bulb puts out about 2000 lumen.. thats why I said it would be difficult to expain light needs by lumens per square inch.

 

[czcz]

Wisteria needed around 2wpg to grow in my 10g fuge, and now it grows fast. Under <2wpg and CO2 the lower leaves died off, and the plant grew slowly. For me java moss looked best under lower light than med light; now it doesn't get any denser, just grows and dies at the same rate. I don't understand this.

How about a daylight bulb and replacing wisteria with java fern, anubias sp, or crypts?

HTH
--

So why not just measure it in watts per square inches of surface area?

Watts are a measure of consumption; lumens are a measure of light. Incandescent lights are considered less efficient than flourescents because they have less lumens per watt, for example.

It is important to realize these and other formulas and metrics attempt to quantify experience. People with small tanks following general wpg rules found problems with growing high light plants. Check out the lighting over the small AGA competition tanks.

FWIW, I'm finding this true of med/high light plants, but not low light plants.

 

[krap101]

hmm back to the candle thingy, how did they decide which candle to use? because ive had candles that burn really really bright (new) and others they just like 1/2 that size. is there like a lumen candle or something, lol

and is a lumen same thing as like candlepower or somethign like that?

 

[greenmaji]

I think the candlepower is more of a marketing term more then a scientific term.
and the candle thing.. Im sure there was a standard size candle and standard output of that candle back when this rating was invented (likely a very long time ago). how about using google..

 

[Skyrmir]

http://www.answers.com/candelas?ab=t19

It's the amount of light emitted by a specific amount of platinum at a specific temperature at a specific wavelength at a specific angle. Who knows if they accounted for air absortion.

Seeing as the candela is measured at a specific wavelength (color) it's not so good at measuring a bulbs usefullness for growing plants. the color is a bit off green so it'd be a very un-used wavelength in a green plant. Thus all the other ways to measure light like wattage and Kelvin and Lumens.

As for what's best? A lightbulb that emits the most of the particular frequencies that your particular plants need, and I'd have no clue in that area. I think the Griggs guy that was mentioned earlier has a lot more of a handle on that.

 

[greenmaji]

candela and lumens are differnt units of measurement for the same thing light output and your not likely going to find a millia candela or candlea rating on a bulb.. If your lucky youll find lumen ratings..