# Simple Diagram to Explain Light-CO2-Ferts Relationship



## davemill (May 3, 2004)

In order to answer numerous questions posed at fish meetings and online, I created the attached diagram to represent the Light-CO2-Ferts relationships across the full range of light levels used in planted tanks.

The primary objective was to create a tool for describing successful combinations of light and other parameters, and for debugging problems with the wrong combinations (i.e., 8 watts per gallon weithout CO2).










This was used in a presentation at the Silicon Valley Aquarium Society this last weekend. I've tested the diagram against numerous live questions and online postings, and it does a darn good job answering them. For example:

http://groups.google.com/[email protected]

http://groups.google.com/[email protected]

http://fins.actwin.com/aquatic-plants/month.200302/msg00198.html

So the question is, what do people here think? Is this a useful tool?
Thanks!

The graphic is based primarily on the work of Tom Barr.


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## Zanmato (May 3, 2004)

Not exactly scientific, but a great tool for beginners to start somewhere.

Edit: A table format would probably be easier to read on the X-Axis.


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## jerseyjay (Jan 25, 2004)

Sorry to break the bubble but I disagree with above diagram. I will even take one step further and say that your chart is very misleading and counterproductive to newcomer's education. 

Why ?

Because there are many exceptions and having another "Rule of Thumb" chart is like putting all the topics, comments, suggestions, tips, observations under one line. 

Many of us tell newcomers to stay away from those Rule of Thumb rules since a lot of them are extremely quick to follow them and treat them as THE ONLY Rule of Thumb to accomplish healthy tank. 

Examples:

1. Your picture illustrates that having light above 2wpg and not adding any fertilizers will promote algae growth. 

Well, it is truth but there are many exceptions where such combo could easily promote healthy growth. We don't have to go to far but look at Luiz Navarro's tanks which DO NOT get any Macro additions. Simply Trace elements. Rest is fish waste. His tanks have 3,4,5,6 or even higher wpg levels. Please check the pictures in aquascaping section and judge for yourself. 

If you lived closer to me, I would take you to friend of mine who has NEVER, NEVER, NEVER added a drop of fertilizer into his tanks. Most of them are setup with 2-3 wpg fixtures and only source of nutrients is fish waste. 

2. Your picture illustrates that having light below 2wpg and adding fertilizer 2-3 times weekly will promote algae growth. 

Again, how much of each element ?. Blank statement. 
Those rules fade out when different size tanks come to play. You would treat differently 10G tank vs. 150G tank. 10G tank with 1-2wpg may not promote healthy growth in "extremely demanding" plants but 250G with 1-2 wpg will be just fine and addition of N-P-K would be very beneficial. 

The reason for my reply is not to say that you haven't done your research but rather to point out that generalizing and creating Rules of Thumb is not beneficial and counterproductive. 

IMHO


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## Daemonfly (Mar 21, 2004)

I'd agree. It's a decent chart for a very simple "generic" guide but because yours is based off the "WPG rule", it's only really usefull in the midrange tank sizes, i.e. 55g, for average setups.

My "20 WPG", no CO2 tank deffinately doesn't fit anywhere on that chart


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## davemill (May 3, 2004)

First, thank you to the people who commented, especially Jay Luto for his well reasoned reply.

Jay luto wrote:


> 1. Your picture illustrates that having light above 2wpg and not adding any fertilizers will promote algae growth.
> 
> Well, it is truth but there are many exceptions where such combo could easily promote healthy growth. We don't have to go to far but look at Luiz Navarro's tanks which DO NOT get any Macro additions.


Your point is well taken. Luiz's tanks are certainly doing well, and they prove that his combination of light-CO2-ferts works.

But would you advise a newcomer to start where Luiz is? The entire purpose of this diagram is to illustrate an easy success zone. While I am certain that Luiz is successful outside that zone, and that many others are too, I also assert that more newcomers will have more success with this rule of thumb than without.

Prior to this, we used to hand out a list of links to about 15 of Tom Barr's best postings on APD and r.a.f.p. This adds up to thousands of words of discussion all around the topic of what combinations of light-CO2-ferts work. This diagram does a better job than all those postings of telling a newbie where to start, and that was it's purpose.

Check out the three links in my original post. I assert that the diagram describes the problem those three newcomers had quite nicely, and that they would be well advised to realign their light-CO2-ferts inside the success zone.


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