# why are water changes bad for algae



## Kibblemania1414 (Feb 1, 2011)

water changes gets new water in and the contaminated with algae water out, just the way things work.


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## ridethespiral (Aug 5, 2010)

Algae loves CO2 changes, and water changes provide that. On low tech tanks such as mine where I do not use CO2, water changes allow highly CO2 saturated water to enter the system, giving algae (which grows way faster than plants in most cases) plenty of chance to take hold


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## takadi (Dec 13, 2010)

Probably why my low tech has zero algae. Last time I did a water change was about last year. Also, letting ramshorns run amok also helps


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## Rockhoe14er (Jan 19, 2011)

so is the only reason why plants grow better after a water change is because of the increase level of co2?


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## ridethespiral (Aug 5, 2010)

That and the additional minerals and nutrients in the tap water. Whenever I do more than 20-30% change my plants will pearl and grow more, but so does algae.


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## OverStocked (May 26, 2007)

If all this was true my tanks with 3 times weekly changes would be algae infest, but they are not.


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## mistergreen (Dec 9, 2006)

You can't lump all algae into the term 'algae'... Water changes may help with some types.
Those types are triggered by the excess organics in the tanks while others aren't dependent on that.


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## ridethespiral (Aug 5, 2010)

over_stocked said:


> If all this was true my tanks with 3 times weekly changes would be algae infest, but they are not.



but you're running CO2, I'm not and neither is the op in his lowtech tank, correct? You do water changes to balance out your tank, water changes ruin the balance of our tanks




mistergreen said:


> You can't lump all algae into the term 'algae'... Water changes may help with some types.
> Those types are triggered by the excess organics in the tanks while others aren't dependent on that.



this is true haha, but I'm mainly thinking like thread algae and BBA


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## Rockhoe14er (Jan 19, 2011)

actually i have a high tech Ei dosing planted tank. Right now i only have a little bit of hair algae but i was curious why if you do more water changes this helps decrease the hair algae level.


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## ridethespiral (Aug 5, 2010)

Oops that was another poster, lol.

I find it makes the thread algae in my tank grow more when I do water changes, but it seems everyones tank does something different


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## Indeed (Jan 28, 2011)

ridethespiral said:


> ...it seems everyones tank does something different


Agreed, but if water changes are to control algae then why not just get a UV sterilizer? I use ine and have very very low amounts of algae in my mid-tech tank.


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## DarkCobra (Jun 22, 2004)

It all depends on the quality of the water in your tank and your tap.

If organic wastes are accumulating endlessly in your tank, then water changes = good.

If your tank is balanced and mostly self-sufficient, then water changes = bad.


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## houseofcards (Mar 21, 2009)

I personally do not think the co2 from a water change is causing algae in a non-co2 tank. If anything the tank was under-dosed or not being dosed so the water change removed nutrients that the plants needed, thus slower growth thus the algae. In a co2-enriched tank good co2 causing good or increased growth so the tank doesn't develop algae. Either way it's the decrease in growth that would cause the algae not the water change it's self. I have plenty of non-co2 setups that get regular water changes and never get algae, but I always dose the tanks.


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## MarkMc (Apr 27, 2007)

Probably way too many variables to draw conclusions about water changes and the promotion or inhibition of algae growth. The only _subjective_ conclusion I have come to is that optimizing levels _and_ distribution of CO2 reduces algae growth. For me, pretty much doesn't matter how much NPK + trace I underdose or overdose as long as there are unlimiting amounts of those (when CO2 is good, of course).


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## Dave-H (Jul 29, 2010)

It seems to be a wild statement to simply say that water changes cause CO2 fluctuations that cause algae. There are so many opinions just on this forum, and there seems to be little qualified scientific opinion on the matter.

Is it even agreed, let alone proven that this is the case? With so many 'reasons' for algae going around, I just don't think any of the many theories hold water on their own.


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## Rockhoe14er (Jan 19, 2011)

Alright is this a fact or a myth "plants grow better after a water change" 

isn't that a reason why water changes would be bad for algae? 

or is there no evidence to support this claim


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## OverStocked (May 26, 2007)

The trouble is you are linking disconnected things. I do not think the plants necessarily grow BETTER after a water change. I think what water changes do is help to prevent the excessive build up of fertilizer, organic waste(mulm) and other "things" in the water. Hormones, etc are all present and in much higher levels than natural systems. We have little proof that they matter, but have plenty of proof that water changes help keep systems healthy. 


Water changes do not cause algae, and they really only prevent it in the sense that they help prevent excessive organic build up. They do a little bit of a "reset" to the system as well. 

I think we are looking for an answer to a question that is unrelated.


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## MarkMc (Apr 27, 2007)

As myself and others have said you can't make factual statements because we only have our own tanks to draw conclusions from and there is no control over conditions from my tank to your tank and his tank and their tank ect, ect. To make this statement one way or another somebody has to do a scientifically constructed experiment or refer to a study that has been done in the past using the "rules" of science. Just because someone does a water change and "thinks" that algae growth has increased cannot conclude that wc's caused algae or prevent algae. We only can tell what we observe in an uncontrolled environment such as our own tanks.
But...that is only an observation-not proof. At any rate I think most folks would agree that water changes have a positive effect on fish and plants.


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## Rockhoe14er (Jan 19, 2011)

fair enough great responses guys.


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## houseofcards (Mar 21, 2009)

MarkMc said:


> ... The only _subjective_ conclusion I have come to is that optimizing levels _and_ distribution of CO2 reduces algae growth.


I know you said it's a subjective statement, but increasing co2 won't necessarily reduce algae growth. In order for that to be effective a certain amount of plant mass is necessary. This plant mass is using the co2 to increase it's uptake of organics. So in the end it's the organic decrease IMO that limits the algae not the co2. Water changes are a part of this organic decrease. 

Think about all setups with and without plants. The whole basis of filtration is removing organic content or having the capacity to deal with the breakdown.


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## plantbrain (Dec 15, 2003)

over_stocked said:


> The trouble is you are linking disconnected things. I do not think the plants necessarily grow BETTER after a water change. I think what water changes do is help to prevent the excessive build up of fertilizer, organic waste(mulm) and other "things" in the water. Hormones, etc are all present and in much higher levels than natural systems. We have little proof that they matter, but have plenty of proof that water changes help keep systems healthy.
> 
> 
> Water changes do not cause algae, and they really only prevent it in the sense that they help prevent excessive organic build up. They do a little bit of a "reset" to the system as well.
> ...


How does over fertized tanks stunt plant growth?
How much ppm of a specific fert does that take?
How much organic waste and what fraction of that waste caused reduced growth?

Hormones have no effect on any aquatic planted in terms of growth or repression in aquatic plants(folks have done this).

Things?

What are those?

I think water changes can cause algae in some non CO2 planted tanks, but I do not think they do any harm and if anything, only serve to help a planted tank.

Why?

Perhaps adding rich CO2(some tap is loaded 10-20ppm etc, some less so 1-4ppm), perhaps breaking up the boundary layers, or exposure to air allows a quick up take of CO2(these are fairly reasonable reasons to see some effects in some tanks, whereas others might not).

How can not doing water changes in a non CO2 tank prevent algae in some tanks and doing water changes in others help? It does not seem logical or reasonable to suggest that both occurs for opposite reasons.


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## plantbrain (Dec 15, 2003)

houseofcards said:


> So in the end it's the organic decrease IMO that limits the algae not the co2. Water changes are a part of this organic decrease.
> 
> Think about all setups with and without plants. The whole basis of filtration is removing organic content or having the capacity to deal with the breakdown.


So why does this not apply to non CO2 tanks where no water changes are done for months or longer?


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## plantbrain (Dec 15, 2003)

MarkMc said:


> As myself and others have said you can't make factual statements because we only have our own tanks to draw conclusions from and there is no control over conditions from my tank to your tank and his tank and their tank ect, ect. To make this statement one way or another somebody has to do a scientifically constructed experiment or refer to a study that has been done in the past using the "rules" of science. Just because someone does a water change and "thinks" that algae growth has increased cannot conclude that wc's caused algae or prevent algae. We only can tell what we observe in an uncontrolled environment such as our own tanks.
> But...that is only an observation-not proof. At any rate I think most folks would agree that water changes have a positive effect on fish and plants.


Actually one does not need a rigorous scientific test to answer many things in the hobby. But...you do need a reference control and you do need to actively attempt to falsify the hypothesis, which few aquarist bother to do.

For a reference control you also need to have the skills to be able to produce a reference tank to start with, without that, one cannot say much of anything nor draw any conclusions.

Example:

A PO4 rich tank(say 5ppm PO4) without algae.
If the tank lacks algae, several others also report the same and over time, and has high PO4 as well, then it is reasonable to suggest that PO4 alone cannot induce algae blooms over time.


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## plantbrain (Dec 15, 2003)

over_stocked said:


> I think we are looking for an answer to a question that is unrelated.


roud:

Yep.......


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## mylittlefish (Oct 5, 2010)

Phosphate Levels....... Use to be a big topic?????

No one tests for those anymore.


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## OverStocked (May 26, 2007)

plantbrain said:


> How does over fertized tanks stunt plant growth?
> How much ppm of a specific fert does that take?
> How much organic waste and what fraction of that waste caused reduced growth?
> 
> ...


I didn't say that fertilizers stunted plant growth. The reference to hormones was not plant related, but in reference to part of why we do water changes for fish. There is good reason to do water changes for both fish and plants. 

THe "things" I inferred were the hormones and some layers of unknown in comparison to natural ecosystems.


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## houseofcards (Mar 21, 2009)

plantbrain said:


> So why does this not apply to non CO2 tanks where no water changes are done for months or longer?


I think you and I both know that there are very few absolutes in this hobby. There will always be a set of parameters that exist where the tank is working fine based on it's given variables. But if you took a typical tank with a typical light, stock/feed, plant load and dosed the tank, it would be very difficult for me to believe that you would do better with such a tank if you didn't do regular water changes vs one that did. 

Why would the co2 from a water change cause algae in a non-co2 tank. Why would the flux alone cause the algae? If the tank wasn't dosed enough and the water change removed nutrients needed, then yes I could see that happening since the plants would be limited, but if the tank is dosed enough I couldn't. Wouldn't this hold true for all the co2 tanks that receive a massive water change every week lowering the co2 temporarily?


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