There is no one single reason.

NH4, vegetative vs sexual reproduction, CO2, light differences etc all play roles with specific species of algae.

NH4 induces algae whereas NO3 does not over a an extremely wide range.
Too little PO4, NO3, Fe etc can induce algae as well, as can variations in CO2 ppm under higher light.

So too little nutrients can induce BBA, GSA, GDA, BGA, hair algae.

Not so much excess.

Algae have been around a long time, they have little reason to worry about plants outcompeteing them, they will wait till the plants die back and then they will take over in natural systems and many natural system don't have plants anyway, there's not enough nutrients to support them.


Plants namely grow fast when they have lots of light/CO2 and nutrients.
Just like in our tanks.

More plants=> less algae.

Algae have spores waiting and hanging out till things get good and the environment is ripe for them to grow well.

Plant seeds and algae spores just don't sprout and germinate for no good reason.

These are adaptations to get through tough times ahead.
Most desert plants are annuals and bloom only after a rain.

Algae, same type of thing, you add NH4, which is a good indicator of good growing conditions, and the algae will take off.

Some algae like lower nutrient levels before spores germinate, some like it when CO2 is all over, some when PO4 is low etc.

I'll go into detail later about all that, it's a 2-3 part series on algae I'll write up.

Regards,
Tom Barr

ok, thanks

so, did you speak to Ole about alleleopathy then Tom? Troels was there as well, perhaps he had thoughts on the matter?

We agree on most everything each have said. I've spent the last 3 days with them taking them all over the Bay area and 2 with Karen.

It's the rest of hobbyists that have disagreements and issues

Regards,

Tom Barr

By the way, after speaking with several researchers in aquatic botany, I've been unable to find critical in situ CO2 measurement like the readings I got from the CO2 meter probe.

No one has really ever done a good study using it in natural systems.

Seems like they'd want to measure the most typically limiting component of submersed plant growth.

Give what we know about morphology, flow and CO2 differences in our tanks, a simple issue like differences in CO2 uptake between species would be a strong reason for one of those species not to do well together. Many claim allelopathic reasons. I've never been able to show this even with 300 + species. Some critics have claimed perhaps I just needed higher biomass of one or the other species, but this does not seem like that valid of an argument.

If it where, typically with allelopathic chemicals, we see a a strong response over a wide range of concentrations of that chemical on the susceptible plants. In otherwords, the concentration is less important.

Still, some plants are far more aggressive at CO2 uptake than others.
This can be measured and has been. Given the large role CO2 plays and at limiting levels, this can really have a dramatic effect.

It seems that this issue, rather than allelopathy, whether it is plant=plant or algae - plant is really the main driver.

To test this, we can (and many have), manipulated CO2 and have had repeatable and strong responses from plants. Some die etc, most get algae.

With allelopathy, we can test using ACTIVATED carbon to remove any alleopathic chemicals, again, many have done this and no one has EVER reported a correlation between algae and using activated carbon that I or others are aware of.

So given the observations and simple test a hobbyist can do and draw from, this entire idea, while perhaps a sexy idea, is pretty weak in it's logic, experimental results, and the research which shows little(no) support to date in any natural system.

Questions arise about how to tease apart the other causes to poor plant growth, algae blooms etc, these must be addressed and ruled out before being left with some pie in the sky theory.

Little by little, test by test, year to year, you pick away at the questions and get around to testing it and seeing.

Somethings might require $$ equipment, some can be explained well using basic hobbyists planted tanks and test.

Regards,
Tom Barr

I recently attended a lecture on allelopathy by Elisabeth M. Gross the leading researcher on alleleopathy in Europe.
She's written a paper(one of many) named ' Alleleopathy of Aquatic Autotrophs'

Very interesting read..

it can be found in:

Critical reviews in Plant Sciences 22 (3&4):313-339 (2003)


or I can scan you a copy from work, if you haven't got access to the paper.

Hi,
I think I read it.
I'm sure Ole has as well.

Regards,
Tom Barr