Trying to understand the mechanism of algae supression

Mr. Barr
I've never really understood the reasons that algae are suppressed as a result of proper dosing such as your EI method. To be quite honest, the (Sears & Conlin?) hypothesis regarding limiting PO4 seems more logical to me since it offers a mechanism, or a control variable by which the algae may be throttled. I've read enough on this site to realize that you disagree and that you do not feel there is a direct correlation between PO4 and algal blooms. This is mind bending for me because it seems that most of the ecological studies of agricultural areas equate algal blooms in downstream lakes and waterways with causal factors associated with farm fertilizers mostly containing nitrates and phosphates. I certainly don't know all the facts though so there could be other factors involved.

From what I've gathered, the theory behind algae supression is that when all available nutrients are present in the water column the plants are able to "out-compete" the algae, but what does this really mean? Algae (spores?) and plants are present in the tank concurrently and seemingly have an equal opportunity at any point in time to compete for and to uptake at whatever individual rate each is capable of.

Suppose for a moment that we maintain the band of optimum nutrient levels for the plants, lets say 40 ppm NO3 for example. Let's also suppose that we have plant uptake sufficient for optimum growth, let's say for arguments sake 2 ppm NO3 per day. At the end of the day there is still 38 ppm of NO3 left for the algae to "scrounge" isn't there? The following 24 hour period the plants take another 2 ppm. That still leaves at or near 36 ppm NO3. The same situation goes for all the other nutrients, whatever the plants take there should be plenty left for the scrounging algae. It seems to me an EI treated tank should have both optimum plant growth and algae. Furthermore each plant is competing with the other. There does not seem to be a concerted effort on the plants to gang up on the algae, it's a jungle, with every plant for itself. It would makes sense somehow if the metabolic rate of the plants depleted all the nutrients before the algae could uptake any but this is not the case as there are plenty of nutrients available at any time for any organism to use - which is exactly the point of EI!

When I look at my tank I see just as much or more pearling from the beard algae as from any given plant (well, I assume it's O2 and not some other gas). This leads me to believe, without any formal training in plant physiology, that the algae are functioning in more or less the same way the plants are in terms of nutrient uptake. In my case I'm also speculating that the algae are contributors to the overall uptake rate.

I therefore fail to see why the algae is supressed just because the plants are happy as a result a non-deficiency. I was hoping you could clarify these linger doubts for me.

Would appreciate any insights.

Cheers,

 

Re: Trying to understand the mechanism of algae supression

Hi Hendra,
Yes, I agree with every thing you said; that the algae require less nutrients, that EI focuses more on plant needs etc., but the fact remains that EI is lauded herein because of it's advantage of providing for the plants as well as it's ultimate benefit of reducing algae as a result of plant health.

A review of many posts which begin with "...I have a problem with xyz algae..." reveals that the typical response goes something like "...follow the general concepts of EI, the plants will be happy and within some time period the algae will subside..."

I guess the origin of my confusion is that I see no logical reason for the algae to ever subside regardless of what advantage to the plants the dosing system provides. In fact, it seems to me that just the opposite should occur; as the plants do well so should the algae. Unlike some, I have no reservations whatsoever about dosing more of everything if needed. That's because I inevitably see a growth increase or better colors and so forth. There is however, some gap in my comprehension that leaves me unable to reconcile why, if algae require less nutrients to thrive, should they be unable to survive when we offer them plenty of nutrients? Surely the algae don't realize that all these nutrients aren't really for them!

I can't shake the feeling that there is some other dynamic occurring. You are probably right about shortening the light period, but in a way, even that is illogical to me. As long as the light is on aren't the algae being "out-competed"? What physiological change occurs after 9 hours?

I think you may be right about the unknown process which doesn't permit algae to grow on healthy plants. But then does that mean the health of the leaf/plant cannot be judged purely on the basis of growth rate? Case in point my Hygrophila corymbosa "Stricta". From diminuative plantlets having 1 inch leaves they have quadrupled in girth and sport 6 inch leaves within 3 weeks. They are probably the fastest growing weed in the tank, yet, wisps of thread algae grows at the tips and a thin layer of the mottled dark green slime (easily removed) often covers the rest of the leaf. A similar story for the H. Polysperma and H. difformis. Weekly trimmings of at least 1/2 pound of material yet, algae persists. Are the leaves/plants not healthy?

I'll continue to follow the principles of EI because that makes sense for the plants and because it mitigates the addiction to test kits. I just wish I understood why the secondary effect should be algae decrease.

Cheers,