3 questions - The Planted Tank Forum
Old 10-22-2008, 06:14 PM Thread Starter
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3 questions

1) As I understand lighting, 1 27 watt bulb equals 27 watts worth of light. But 2 27 watt bulbs don't make 54 watts right? I mean it uses 54 watts of energy but still, the light output is still only 27 watts correct? It just spreads it over a wider area.

2) How often do I dose excel?

3) How often do I dose ferts?

Requisite tank info:
*5 gallon tank
*1 27 watt daylight bulb
*I suppose one would consider the tank fairly heavily planted as I have micro swords, anachris, wisteria, hornwort, Jungle Val and banana plants.
*Pure laterite mixed with gravel for substrate.

Thanks!
GinaM is offline

Old 10-22-2008, 06:27 PM
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1) Last time I checked the mathematics out, 2 x 27w does in fact equal 54w. Maybe I'm not exactly sure what you're asking, though. Yes, it's spread over a wider area, but it doesn't negate the doubling of the wattage. That's why the amount of wattage isn't all that's necessary to determine how much light to use... we also factor in the surface area (although people usually use watts per gallon, but that is essentially the same thing as saying watts per amount of space working with).

2) Every day

3) That's a toughie. There are plenty of schools of thought about this. I suppose, the easiest answer is to say just follow the directions on the bottle, assuming you're using liquid ferts, anyway.
Church is offline
Old 10-22-2008, 06:59 PM Thread Starter
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Then what is a more suitable way of determining sufficient lighting? I know 6700K is the right color temperature. But if 27 watts is good for a 5 g, wouldn't 2 27 watts be good for a 10g? They cover the larger area and the tanks are of similar depth. And for that matter would that be low, medium or high lighting? Oh...lighting can be SO confusing! Thanks for your help.

Gina

Quote:
Originally Posted by Church View Post
1) Last time I checked the mathematics out, 2 x 27w does in fact equal 54w. Maybe I'm not exactly sure what you're asking, though. Yes, it's spread over a wider area, but it doesn't negate the doubling of the wattage. That's why the amount of wattage isn't all that's necessary to determine how much light to use... we also factor in the surface area (although people usually use watts per gallon, but that is essentially the same thing as saying watts per amount of space working with).
GinaM is offline

Old 10-22-2008, 07:05 PM
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http://www.rexgrigg.com/mlt.html

^ give that a read-through first.
epicfish is offline
Old 10-22-2008, 07:27 PM
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Quote:
Originally Posted by GinaM View Post
Then what is a more suitable way of determining sufficient lighting? I know 6700K is the right color temperature. But if 27 watts is good for a 5 g, wouldn't 2 27 watts be good for a 10g? They cover the larger area and the tanks are of similar depth. And for that matter would that be low, medium or high lighting? Oh...lighting can be SO confusing! Thanks for your help.

Gina
First of all, 6700K is only ONE of many "right" color temperatures. Anything between 6500K and 10000K is considered appropriate.

Second of all, don't fall into the trap of thinking that watts-per-gallon is a law of physics. It's just a guideline, one which notably does not apply very well to small tanks (anything under ~20g or so?). That being said, in keeping with the guideline theme, YES, if 1x27w lamp works well for a 5g, then 2x27w lamps would work well for a 10g. If you do the math, you end up with the exact same 5.4wpg in both scenarios. But because this guideline is not linear, it's not really accurate to say they are getting EQUAL lighting in respect to their size. I would say that the 5.4wpg on a 10g aquarium is on the lower end of what could be called "high light," whereas the 5.4wpg on a 5g is on the upper end of what could be called "medium light."

Did that make sense?

In other words, when dealing with small tanks, the wpg guideline is not very dependable. It is also said that the same applies to extra-large tanks as well.

One last thing, too. It is highly contested that water depth plays much of a role in the lighting calculations. In indoor terrestrial gardening, distance from the bulb plays a visible role, so I don't know why aquatic gardening would be any different, but many people with light meters claim that there is no discernible difference in lighting a 3 ft tall tank vs. a 18" tall one.

Hope some of that helps ya. I know it's confusing, but you'll get it. Good on you for doing your homework ahead of time!
Church is offline
Old 10-22-2008, 07:31 PM
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Quote:
Originally Posted by Church View Post
One last thing, too. It is highly contested that water depth plays much of a role in the lighting calculations. In indoor terrestrial gardening, distance from the bulb plays a visible role, so I don't know why aquatic gardening would be any different, but many people with light meters claim that there is no discernible difference in lighting a 3 ft tall tank vs. a 18" tall one.
What?

I have PAR meter results that confirm that water depth HIGHLY affects the amount of usable light that penetrates. I've never read a report/post reporting otherwise. Care to link me?
epicfish is offline
Old 10-22-2008, 07:32 PM
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I could have sworn it was something Rex said, or had linked to from his site. I'll try to find it...
Church is offline
Old 10-22-2008, 07:40 PM
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Well, I already found a few threads here at tpt about it, just by doing a search, but nothing specifically like I was remembering. But I did find the place on Rex's site where he talks about it:

Quote:
Ok, I have seen a lot of people repeating the lie that deeper tanks need more light. That might be true if you are using crappy lighting systems or barely have enough light as it is. But if you use decent lighting systems with decent reflectors the depth of the tank doesn't mean squat. You might hear about spectral drop off or lighting decrease. Bull[censored][censored][censored][censored]! If your tank was 30 feet deep it would be one thing.
That was taken from http://www.rexgrigg.com/light.html. But those very same thoughts of his have been reflected here, on several occasions. I'm at work now so it's not that easy to comb through the search results at the moment.

My point is that these thoughts are hogwash. A taller tank will require more lighting than a shallow tank with the same footprint would require. Period.
Church is offline
Old 10-22-2008, 07:40 PM
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Taken from: http://www.nano-reef.com/forums/inde...owtopic=168811

Quote:
The top readings were taken just below the surface. All of the other readings were taken directly below the reflectors where possible. Most of the other readings show the depth where it was recorded and the number is shown at the relative position (left to right) where it was recorded. These readings are simply the PAR number the probe showed at that spot in the aquarium.

epicfish is offline
Old 10-22-2008, 07:47 PM
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Quote:
Originally Posted by Church View Post
My point is that these thoughts are hogwash. A taller tank will require more lighting than a shallow tank with the same footprint would require. Period.
If you compare two tanks with the same footprint, one 12" tall and one 30" tall, better reflectors would play more of a role thanmore light. I think that was Rex' point...quality vs. quantity.

For example, if you have 100 watts vs. 200 watts of CFL screw-in lighting over the 30" tall tank, it's still not going to reach the bottom. But if you use T5HO bulbs with highly polished MIRO 4/7 individual parabolic reflectors, you may only need 100 watts to grow what you want.
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Old 10-22-2008, 07:59 PM
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This was just one example. I'm telling you, this has come up rather frequently, on multiple different message boards. And I'm not in agreement with that line of thought in the first place.

I've been growing vegetables, herbs, and other houseplants indoors under fluorescent lighting pretty much my whole life, and it's beyond evident that distance from the bulbs affects plant growth. It's never been a question in my life, and I'm always surprised to see people contesting this.

I don't own a PAR meter. But in the words of Bob Dylan, "you don't need a weather vane to know which way the wind blows."
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Old 10-22-2008, 09:00 PM Thread Starter
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Ahhh...here is what I was getting at...This quote was taken from the article "Basics to starting a Planted Tank" on this very website.

Example: Take a 10 gallon tank, by the math you could put 2 - 18 watt Normal Output Flourescent bulbs over it and have 3 + WPG "mathematically" but you still only have 18 watts of "intensity. You will not be able to grow many varieties of plants successfully in this tank even though you are at the 3 WPG that we are looking for. Now if you take that same 10 gallon tank and put a 1 X 36 watt Compact flourescent over it you now have the same amount of watts total but you have 36 watts of "Bulb Intensity" in which you can grow virtually any plants you choose.

https://www.plantedtank.net/articles/...lanted-Tank/4/

But the "intensity" of the bulb is what I was asking about with 2 27 watts bulbs still only equaling 27 watts. I hope that makes more sense now.
GinaM is offline
Old 10-22-2008, 09:07 PM
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Poorly worded.
epicfish is offline
Old 10-22-2008, 09:08 PM
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i must say that i have never heard this

strange that it is on the "basics" page

cant say im an expert, i've just never read this anywhere else
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Old 10-22-2008, 09:11 PM
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Okay, that makes more sense now that I can see it in its original context... I think you are overthinking things, actually. Basically, this just corresponds with the reasoning behind why the wpg guideline falls apart in smaller tanks: sure, you can obtain a high wpg number, but if the source bulbs are only 9w or 15w, it's going to be low light, no matter what. But a 27w bulb is nothing to shake a stick at. That's actually rather intense lighting.

But try not to think too much about "intensity." Just know that if you want to grow most plants, you won't be able to do so with lower wattage bulbs. But since no one recommended for you to get a Coralife mini-Aqualight (2x9w) fixture, it just never came up. Once you started talking about a 27w lamp, that became a non-issue. If you had said "Do three 9w bulbs create the same amount of light as one 27w bulb?" the response would have been "no."

I hope that helps a little.
Church is offline

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