How do plants "outcompete" algae in a fertilized a

[hashbaz]

How do plants "out-compete" algae in a fertilized aquarium?

I understand the general practices here, but don't understand some of the science behind them.

In your high light aquariums, you are constantly dosing nutrients. I assume that between dosings these nutrients never drop below certain levels. This gives a tank with lots of light and lots of nutrients. In my thinking - if there is lots of light, and lots of nutrients there will be lots of algae regardless of how many plants are in there.

Do nutrient levels drop low enough between dosings that the algae dies, while the plants live off reserves? Or are there other nutrients in the water (not dosed) that are consumed/eliminated by the plants? Or am I just missing something here?

 

[tetrin]

i think the key word is CO2. high quantities of dissolved co2 probably acts as an inhibitor to nutrient access by algae, and conversely, help plants. but i'm not sure .

 

[malkore]

CO2 inhibits algae, thats for certain.

However plants also produce allelochemicals, which is a form of chemical warfare. plant A's allelo's will stunt plant B's growth to a very small degree...but will stunt algae severly.
but if the plant is not happy and growing optimally, it doesn't produce those chemicals, and algae quickly gains a foothold.

Its like humans...when we are healthy, we can fight off the cold virus easily...but if we're a little tired, that virus quickly latches on.

 

[jrp1588]

CO2

but if the plant is happy and growing optimally, it doesn't produce those chemicals, and algae quickly gains a foothold.

So your saying when a plant is totally healthy and satisfied, it doesn't produce its chemical defenses and algae takes hold. So should you keep your plants always wanting a little more...I don't get it.

 

[malkore]

nope, typo, which I just edited to correct. when plants are NOT getting everything they need, they stunt, and don't produce as much of the chemical warfare.

 

[jrp1588]

Ok, ok. You had me confused there for a second. Some of the rules of plant growth seem counterintuitive, but that just seemed crazy.

 

[hashbaz]

Thanks Malkore, I didn't think of "chemical warfare"

 

[malkore]

Yep, one missing word totally screwed up what I was saying, and that's why I edited the original, so anyone skimming this will get hte right info

I think its Diane Walstad's Ecology of the Planted Aquarium that really discusses the effects of allelochemicals on algae, and between plant species. its similar to the chemical warfare that corals use in a marine tank...and is where I hijacked the phrase.

 

[Jchillin]

Thanks for editing that Malkore...that had me going all day yesterday. (hmm...so, if my plants are dying, they will out compete the algae and if they are doing well, the algae will take over.)

 

[Steve Hampton]

I think the first issue regarding how plants "out compete" algae needs to be properly addressed. Plants and algae do not compete. They occupy two different niches. Competition requires that they both occupy the same niche. It should be readily apparent that inorganic nitrate, potassium, and phosphate doesn't cause algae, yet those are the elements needed in abundance to grow healthy plants. The problem for years was the belief that limiting NPK would control algae...but algae can survive and much much less NPK than plants. So limitation only serves to stunt and harm plants. Ammonia/Ammonium and organics are the big causes of algae and is the niche algae occupies. Planted tanks that have no ammonia spikes and low levels of dissolved organic run algae free almost with regard to even very high levels of nitrate, phosphate, and potassium.

Does allelochemicals have an impact? Possibly, but only in tanks that never get water changes like those described by Ms. Walstad. For other tanks the water changing routine will keep the allelochemicals (if the plant actually produces such) diluted to the point of insignificance. There's very little controlled scientific research to prove which plants do and do not use "chemical warfare" and those that do, how concentrated the chemical needs to be. While allelochemicals may play some role in nature it's still highly debatable as to there role in planted tanks.

I know that changing 50-70% of the water weekly in my planted tanks should dilute and chemicals produced by my plants. I've changed larger amounts and one would think that if allelochemicals were what was holding back an algae outbreak then doing these large waters changes would reduce/remove the allelochemicals and cause an algae outbreak. From my research and my experience if you have healthy plants combined with moderate bio-loads and low organics you'll have an algae free (meaning no visible nuisance algae) tank. Large water changes after pruning, no substrate disturbance without large water changes, and quick removal of decaying animal or plant matter will eliminate possible ammonia/ammonium spikes and keeps dissolved organics low.