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So, why does New School = no algae?

86727 Views 128 Replies 57 Participants Last post by  JustLikeAPill
The discussion on the PPS thread got me thinking again. I know it's been discussed before. I don't think we have a definitive answer so lets give it another whack, college try, that sort of thing...

New school fertilization methods (EI and PPS) have certainly deepened our understanding of planted aquarium nutritional dynamics. They have allowed MANY more people to enjoy algae-minimized tanks.

The question is: why do EI and PPS minimize algae?
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IMHO I believe the reasons behind these methods are that the plants are no longer limited by any nutrients. And as long as the plants are growing the algae is kept at bay. Not very scientific, but my experience (see below) from the last 2 years have let me to believe this.

When I started keeping planted tanks, I read about the Sears and Colin paper about limiting Phosphates to stop algae growth. We'll I tried that for a few months and always had BBA and fuzz algae. I kept the NO3 at about 10ppm and the PO4 below .5 ppm. While trying this method I got a bad PO4 test kit that was giving me high readings. We'll I dosed at higher levels of PO4 (still thinking I was at .5 ppm) and the algae was getting less and less. My LFS in Arkansas tested my water and confirmed that my PO4 was over 2ppm. I got me another PO4 test Kit (La Motte) and Once again started the .5ppm Dosing and then the algae once again started appearing. I had to move to South Carolina so the tank was torn down.

In South Carolina I set everything up again and by now I had read about the EI method. So I started using it, and it working nicely. I had good plant growth and very little algae. I test almost daily (I Like to do it). And got a hold of a Bad NO3 test kit and instead of keeping up with the EI method, I believed the test kit more and so I dosed less NO3 than I should have. We'll once again the algae came back. Once I figured that the NO# test kit Was bad. I gave up and bought all La Motte kits.
Once I started to dose and keep the NO3 at about 20ppm and the PO4 at about 2ppm the algae Once again stopped growing. We'll it was Time to move again so I had to tear down the tank once more.

I set up the tank in Florida and everything was going great nice plant growth and no algae (EI Method). I now tested only once or twice a week and just dosed .5 tsb of KNO3 and 1.5 ppm of PO4 every other day. The test kits showed an average of about 20-30 ppm KNO3 and PO4 was always above 2ppm.
I recently had a mishap in the tank. After a water change for some yet unknown reason I lost about 70% of the Fish and about 50% of the plants. The plants that where left had stopped growing. And in a one week period I started seeing algae growing again. About 2 weeks after the mishap All the old and new plants where growing nicely again and the Algae stopped growing.

So from the above experience I concluded that any time the plants stop growing. Due to Lack of nutrients or for some other reason algae will quickly appear. Thats why the methods work they keep the nutrient levels that the plants need.

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And as long as the plants are growing the algae is kept at bay
I believe, correct me if I'm wrong, that the whole purpose of this thread is the question why this is true: Why does unlimited nutrients and happy plants keep algae at bay?
Thanks Alex!

I agree with you that using the new methods results in algae limitation. The question I have is WHY do they work? If plant's growing well = algae limitation AND if algae and plants need the same nutrients (careful, I didn't say in the same ratio, levels, etc.), then can I conclude the following?

Good plant growth = algae limitation BECAUSE:

1) Good plant growth results in limiting a key nutrient for algae; or
2) Good plant growth produces some sort of allelochemical that limits algae?
defdac said:
I believe, correct me if I'm wrong, that the whole purpose of this thread is the question why this is true: Why does unlimited nutrients and happy plants keep algae at bay?

There's a lot of very experienced and knowledgeable folks here. Let's hear your hypothesis, theory, conjecture, what not! You don't have to be right, just throw up your gut feeling.
Why ask why?
S said:
Why ask why?
Because it is key to deepening our understanding of planted aquarium dynamics.
I'll hazard a guess just to keep this ball rolling.

I'll propose that the higher oxygen levels in a tank where the plants are doing well acts to suppress algae. How? Um, maybe the algae is so small that it gets oxidized? That is, the oxygen molecules tear it apart?

Someone like TBarr will probably come along and say "No, I've tested tanks with algae and no algae and both had the same oxygen level." If, so, then that theory is kaput, but I'd be interested in knowing if the correlation was studied.

Hey TW, do you know Hanns-Jürgen Kraus? He's a person who suggested something similar to what you just did. Very controversial back in 1995-6. I have a few of his books and articles. We tried to get them translated and published here but it was a no go.

We discussed it on the APD back in 1997 if I recall. I remember Kaspar Horst of Dupla thought that Kraus' oxygen theory had been disproved. It appeared in Das Aquarium I think.
Hey Art,

No, not familiar with any of that. I just pulled this out of my, um, made it up out of thin air. [smilie=d:

Why do these methods work in contravention of what seems to be found in nature?

Using simple aquarium test kits, I have measured PO4 and NO3 levels in healthy lakes which support an abundance of aquatic plant life. The PO4 and NO3 levels were too small to be measurable - nothing like as high as the levels commonly encouraged in the planted tank hobby. In these locales the lake water was very healthy, clear, not eutrophic. Algae types were neither dominant nor obvious.

While it is difficult to compare a natural environment such as a lake with an aquarium - lakes have thermal zones, areas of run-off, large dilution factors, large surface areas for gas exchange, relatively cool temperatures, and other features that aquariums do not have - the main difference I notice is that lake water is ALIVE. In aquariums, it has a tendency to become DEAD quickly, particularly as a result of chemical manipulation by the inexperienced aquarist.

IME / IMO it is all about water quality rather than nutrients - at least that is the way I tend to analyze and understand the problem or avoiding algae.

Algae prevail in DEAD water. Water changes rejuvenate the system. EI-style, which evolved in times before many people had spreadsheets etc, uses targeted dosing levels and water changes to ensure water quality is optimum. Water changes allow for unknowns to be addressed and buildups to be avoided. PPS is an analytic approach which hinges on providing enough but not too much, so as to ensure optimum water quality while having minimum water changes. When a PPS proponent fails in his/her dosing regime, they do a water change.

Nutrient dosing is just a part of the water quality story.

(Now if only that SAVE AS DRAFT button was down there I could have saved you from reading this embarrassing Plocher-like plonk).

Andrew Cribb
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pineapple said:
IME / IMO it is all about water quality rather than nutrients - at least that is the way I tend to analyze and understand the problem or avoiding algae.

Algae prevail in DEAD water. Water changes rejuvenate the system.
Yeah, but -how- does water quality affect algae? How does a water change 'rejuvenate' water in a way that's bad for algae? What is the specific mechanism? At some point, doesn't this have to come down to a molecular level where the chemistry for algae life processes don't work any more? Just spitballing...

Molecular level research is beyond the means of most hobbyists. Water is a complex media in which chemical reactions take place and solutes are transported. An aquarist has the ability to observe results of some of these changes but usually cannot understand the complex chemistry involved since the methods and tools to investigate these things are not available to him/her.

To say one compononent of healthy water is more or less responsible for the prevention of algal growth seems irrelevent. Healthy gas exchange, low particulate content etc... all contribute to healthy water. If there was one magic component (such as your suggestion of oxygen) responsible for slowing or stopping algae growing, it would have been found before now by better equipped researchers.

Andrew Cribb
I don't understand the chemical processes involved when dosing NPK, but I can dose them to the 'right' levels without any knowledge of molecular biology.

I agree that the water chemistry of an aquarium is complex, and I'm not defending my proposal at all here, it was just a thought. Art can correct me if I'm wrong, but I thought the point of this thread -was- to get to specific causes. If we're going to settle for 'rejuvenated' water then we have to open the door to Plotcher again. :toimonst:

Tom, does it then boil down to a competition between plants and algae? The reason people say you have more wiggle room with less light is that deficiencies can occur quickly when creating a high metabolic rate as is the case with higher light levels. This would imply that it's a nutrient competition thing again.
I'm curious if any of these studies, and the discussion, has taken seasonal changes into account. Is it possible that the varying day lengths,temperatures and thermoclimes, mixing,etc. may have an effect on different species of algae either inhibiting others or out competing others and then making their habitat incompatible for themselves?
Anyone have links to these studies? Would be interesting reading!
Approaching the problem from the converse: if someone were to start a thread on "How to grow really good algae in a planted aquarium" the consensus might be better.

Andrew Cribb

Can a post mortem be performed on algae? If a tank with algae is turned around and it all dies out, can it be put under a microscope and the cause of death determined? Might make a good TV crime show...

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