Dustymac

I understand what he's saying but I don't understand why. Why won't the algae take advantage of the increased nutrient level right along side the plants? What prevents algae from using the increased CO2 to its own benefit?

Jim

Tex Gal

I believe the plants use it up faster. The algae gets starved out. That's my understanding.

aquabillpers

Hey, man, I am me and no one else. LOLOL

Bill

aquabillpers

Here's a link to the thread at Tom Barr's site in which the role of CO2 and algae control is discussed. http://www.barrreport.com/general-pl...ae-growth.html

I don't believe that there is any answer to the question, "Why does increasing the CO2 reduce the amount of algae?" I asked the question there and didn't get a firm answer. In fact, that hypothesis has never been proven in a controlled environment, as far as I know.

Algae requires far fewer nutrients than do macrophytes and it responds faster to an increase in nutrients. It seems unlikely that macrophytes respond fast enough to a change in nutrient levels to outcompete algae.

If nutrients are limited, the algae gets what there is, first. Increasing the CO2 level, if it is limiting, will benefit the algae, at least in the short run.

El natural aquariums by definition do not add CO2, and many of them are algae free. Algae outbreaks are due to nutrient and lighting problems. The outbreaks are remedied by fixing those problems.

Bill

queijoman

Thanks for the tip. The java fern isn't actually buried. It sinks so I put it on top of the soil. That one is my first plant that I bought over a year ago and it has 3 khuli loaches that live in it's "nest"

Dustymac

I think that's pretty close. Definitely the algae gets starved out. I think increasing the CO2 raises the metabolic rate of both plants and algae. Everything starts growing like crazy, pulling on other nutrients to keep up. Before CO2 was the nutrient limiting growth. Now it's some other nutrient.

Plants do have an advantage - they can get some of their nutrition from the substrate. Algae must get their nutrients exclusively from the water. Eventually the plants and algae will scrub the water of one essential nutrient. The plants can recover that nutrient from the substrate and keep growing; the algae can't and starts to wither.

And it's very easy to see how this myth got started. Some aquarist somewhere started a couple of tanks at the same time and they both came down with identical algae problems. For whatever reason, this mythical aquarist decided to try CO2 on one of the tanks and voila! The tank getting CO2 clears up in three days and it takes the other tank two weeks before the algae starts to fade. Of course, our aquarist thinks CO2 killed the algae when in fact all it did was hasten an inevitable death.

Along these same lines of thought, it's easy to see why there is so much confusion surrounding algae and water changes. If you get algae and you have tap water that's bereft of the limiting nutrient, changing the water will dilute that nutrient so it's natural to think changing the water hurts algae. On the other hand, in the same set of circumstances, if your tap water is flush with the limiting nutrient, changing the water will replenish that nutrient leading to a chronic and frustrating algae problem.

At least that's what I think.
Jim

PS. Oh, and Bill? Mom says it's your turn to take her shopping this week.

aquabillpers

You are assuming that CO2 is the limiting factor. What if it isn't? Lots of aquariums with plenty of CO2 have algae problems.

Algae doesn't need as much nutrient as do macrophytes, and they are faster to respond to changes, like the addition of a limiting nutrient. The myth is that plants can outcompete it.

How do you know that? Who was that myth starter? Did he say anything about plants outcompeting algae?

Some of us have a tendency to develop a hypothesis and then state it as if it were a fact, even though it hadn't been tested. There has been research done on this subject; check out that Barr Report thread I quoted earlier to read about it.

LOL. Being slow, it took me a while to get that!

Bill

Philosophos

I don't think you will necessarily get out of line. I just spent hours of my time debating with someone over on another site (it's a popular one in the hobby; no names) yesterday though, and the thread got shut down because some moderator decided that the debate was full of personal insults. Neither I or the person I was debating with could see any, and we had a bitter laugh about it after. Over-modding has caused me to waste hours of my time, so I'm starting to prefer my debates in places with laxer rules.

Anyhow, it looks like TexGal is posting in with this one so there shouldn't be issues; I've never seen her over-mod a thread.

I don't think there's any good tautology showing why CO2 prevents algae. I think there are some decent theories, and a corelation that is too consisten to say that co CO2 isn't at least a related mechanism. You call it a post hoc, but in fact our entire existence consists of a post hoc ergo propter hoc fallacy; it's a matter of the stringency to which we examine the topic. Tons of people are turning up CO2, turning down their light, and getting tanks with a lack of algae with quite reasonable consistently.

I am talking about allelopathy as a possibility though, despite what Texgal said. I'm not talking about plant killing plant through elevating the phenol levels and such throughout the entire colulm. I don't think that a healthy tank should have enough decaying plant matter to manage something like that.

There are a number of books and papers touching on the subject. Here are two outlining the concept, I can toss out more instances if you'd like:

Hypothesis that allelopathy is used against algae, but why it is difficult to prove:
http://books.google.com/books?id=gl7...age&q=&f=false

An example in a natural system. I don't think it's possible to get column levels in the tank high enough to make a difference (look around for Ole's Refute for allelopathy), but at the point of release it may be in high enough concentration before being dilluted by the column:
http://www3.interscience.wiley.com/j...TRY=1&SRETRY=0

This is the best theory going right now. If I were bothered for conjecture, I would say that perhaps aquatic plants retain a bit of a cuticle under water and that sheds, or perhaps part of the upper epidermis sloughs off slowly. Both would provide metabolism-based reasons for plants to resist algae. As it is, I lake the equipment to test any of these ideas.

-Philosophos

Tex Gal

Sorry Philo. for speaking for you. I know you can surely defend your own arguments. Glad you're speaking up again.

So many of these debates continue over and over again. I guess if the hobby turned into a lab full of scientists with control tanks and such we may be able to settle some of this. Since my goal is to have healthy algae free tanks, I try to do what has worked for others, despite the science behind the method. Some of these methods just work most of the time, as Philo. said. That's good enough for me. My tanks are healthy, my plants are growing like weeds , and my fish are spawning. The world is a good place!

Philosophos

Don't worry about it Tex; plenty of people know how I feel about allelopathy as a column-wide issue. This localized leaf level thing is new to me; it's a hole I've seen in Ole's refutation to allelopathy.

Actually Tom Barr spent a crapload of time trying to induce various types of algae, in part to refute the PO4 myth, and at the same time did some good work showing that algae didn't thrive on plants with non-limiting levels of CO2. This is somthing witnessed repeatedly, and reproduced in many high tech tanks. This relationship between the two is something I would be shocked to see disproven. The exact methods may not be precisely known, but there are some theories out there based on knowledge of plants that already exists.

I'm not sure who got the hairbrained idea that CO2 is directly toxict to algae; there's absolutely no evidence for it. The relationship between CO2 and algae is definitely indirect, and almost definitely through the plant. High CO2 and non-limiting nutrients doesn't help to eliminate the spread of algae on driftwood or glass after all

-Philosophos