Watt confusion - The Planted Tank Forum
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post #1 of 16 (permalink) Old 09-27-2003, 06:54 AM Thread Starter
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I'm new here but I have had a rather successful 5.5 gallon planted tank for a while (over two years, I think). It's lighted by a 14 watt NO plant bulb, and contains crypts, sags, duckweed and javas... The plants even pearl once in a while. There are currently two killies in there, and a small powerhead to provide movement. No filter. Fluorite substrate. And lots of pruning that I've been putting off. :P

My issue is, I've been reading on this board that my tank is underpowered when it comes to light! Apparently, my 2.5 wpg isn't considered enough... and that I should aim for 5wpg or even higher. WHY does the rules of wpg break down when it comes to smaller tanks? HOW? According to this rule, my plants should be languishing, but they're clearly not.

I'm starting another 5.5g tank in my bedroom... This time it has a 13w CF bulb in the fixture. According to this board again, a PC bulb is twice as efficient as a NO bulb... Thus, I actually have 26 watts over my tank... which brings the lighting to 4.72wpg. Is this right??? Again I'm going with no filter and a powerhead for water movement, along with a Fluorite substrate. Not sure what I'm going to plant, tho. But if I have almost 5wpg in there, does that mean I have to fertilize and add CO2?

Heeeeeeeeeeeelp meeeeeeeeeeeeeeeeeeee..........
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post #2 of 16 (permalink) Old 09-27-2003, 07:57 AM
2la
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Your plants are not the demanding species people are thinking about when they say the wpg rule breaks down for smaller tanks. Your plants could probably survive on ambient light alone, if situated near a window.

As for why the rule breaks down, can you imagine growing something like Rotala macranda under a 3-watt bulb? What if it was in a 1-gallon container? You end up with 3wpg, but the absolute amount of light is clearly insufficient for growing such a light-needy species.
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post #3 of 16 (permalink) Old 09-27-2003, 10:23 PM Thread Starter
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So if I wanted to grow rotala in a 5.5, I'd have to upgrade the light to a CSL 32 watt smartlight with a day lamp? Plus the CO2, fertilizers, etc etc...?
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post #4 of 16 (permalink) Old 09-27-2003, 11:17 PM
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I'd say something closer to 20W would be sufficient because of the shorter height of a 5.5-gallon tank. But yes, the CO2 and fertilization would probably be absolute necessities for growing this plant well.
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post #5 of 16 (permalink) Old 09-27-2003, 11:28 PM Thread Starter
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That's very interesting. So what about the 13 watt compact fluorescent? Should I count that as double the wattage compared to regular fluorescent?
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post #6 of 16 (permalink) Old 09-27-2003, 11:33 PM
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I don't think so. I know there is an increase in intensity from a CF bulb compared to a NO one, but I think a fudge factor of 2 is overestimating it.
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post #7 of 16 (permalink) Old 09-27-2003, 11:37 PM Thread Starter
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*snicker* Oh well.
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post #8 of 16 (permalink) Old 10-23-2003, 12:38 AM
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First if the CF is 13 watts thats what it is-period. The beauty of them is that they are smaller and throw out higher wattages for its sizethan other lamps.For a 5gal to grow rotala if its indica (rotundifolia) you can get away with 13 watts easy and no CO2.But for Rotala Magenta or Macrantha you would have to up the wattage to 18watts .You would also need to add CO2 and for that size I would go with the DIY yeast type generation.Also you dont need the powerhead so get rid of it.It takes away any CO2 that might be helpful.Instead hook up a cheap whisper HOB filter for extra water capacity and biological filtration.
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post #9 of 16 (permalink) Old 10-23-2003, 01:16 AM
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Get the one like a whisper for a little 10 gallon because it is good for its size and not move the top of the water at all! This is what I have on my ten gallon tank.
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post #10 of 16 (permalink) Old 10-23-2003, 03:24 PM
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I disagree, if the powerhead and no filter is working fine, why bother changing it. I don't see why you would say a powerhead will cause co2 loss but the impeller & flow of a HOB wouldn't.
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post #11 of 16 (permalink) Old 10-23-2003, 07:46 PM
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well, the only way it would is if there was air bubbles coming out of it, but if not then its fine. Leave it if no air bubbles are coming out.
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post #12 of 16 (permalink) Old 10-23-2003, 10:27 PM
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A watt is a watt is a watt- a measure of electrical power. The efficiency of a light is the amount of light a watt produces. So, a more efficient light is going to produce more light per watt.

Sort of like tube watts (sorry- musician's joke )

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post #13 of 16 (permalink) Old 10-23-2003, 11:04 PM
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I think there is a big misunderstanding about the watts per gallon. I think lumen or even lux would be much more meaningful. But back to the real world...

First off, this only applies to fluorescent light bulbs. Incandescent lights are so inefficient that I consider them just disguised heaters.

On a lumen per watt basis, a T8 fluorescent light will be the more efficient lightsource... creating the most lumens per watt. PC bulbs will appear much brighter, but in a more compact form.

The statement that a 13W PC bulb is twice as bright as a (13W!!) regular fluorescent bulb is incorrect in my opinion. Yes, if you compare a 32W NO with a 55W PC bulb the latter is brighter, but considering the total light output of equal wattage NO and PC bulbs you will get more light out of the NO bulb.

Don't get me wrong... I know that the compact form and usually excellent reflectors of PC fixtures permits to throw more light into a tank. Just the general understanding that this due to a higher efficiency of PC bulbs compared to NO bulbs is wrong IMO.
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post #14 of 16 (permalink) Old 11-03-2003, 01:48 AM Thread Starter
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Thanks for your help, guys. I've decided to have a 10 gallon in my room, with a 32w compact, powerhead with no venturi, diy yeast CO2, and a substrate mix of flourite and plain gravel. So far things are growing like mad and I had to do some major pruning the other night. It's a cute little tank, with 6 amano shrimp to take care of the algae. There are a lot of amphipods and hydra in there, but I'm sure they'll be gone when I add fish. The important thing is that I like it and the plants are growing well and the shrimp are still alive. (How does one tell if a shrimp is sick, anyway?)
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post #15 of 16 (permalink) Old 11-03-2003, 02:24 AM
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Quote:
(How does one tell if a shrimp is sick, anyway?)
They stop moving !! :lol:

FILSTAR Pimp #2

75 gal heavily planted,50/50 Black beauty,Eco-complete substrate, Pressurised CO2 with solenoid, ph controller, AB Reactor 1000, 330 watts 9325K GE PC lighting,Ehiem Liquidoser, 2-Filstar xp3 canisters.
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