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Thread: Does too much phosphate cause algae?

  1. Does too much phosphate cause algae?

    I have read conflicting theories about this and I was wondering if anyone really knows the answer. Do I need to worry about making sure that phosphate is the limiting factor or not? I have both green dust algae and green spot algae in one tank right now which is what got me thinking about whether I should slack back on phosphate in that tank. But then of course my plants are already hurting from the gsa, I don't want to do anything that will make things worse either. I especially don't want to get into bga territory again, I wiped out a whole tank of plants before and literally can't afford to kill anything else.

  2. #2
    No, phosphate is not a cause of algae. In fact more phosphate will usually stop GSA. No nutrient, other than ammonia, is a cause of algae.
    Hoppy

  3. Hm. Should I be dosing something higher to get rid of gsa?

  4. #4
    I dose about twice what the EI quantities are of KH2PO4 to keep my GSA away. I played around with phosphate for several weeks before just giving in and doubling the EI dosage. Right now I am dosing about half of the EI rate, with a rich substrate and relatively low lighting, but I am still dosing about twice the recommended amount, in proportion to nitrate, recommended by EI. I don't claim that this is what everyone should do, or even that it is necessary for me, but it does seem to work for me.
    Hoppy

  5. #5
    Quote Originally Posted by VaughnH View Post
    No, phosphate is not a cause of algae. In fact more phosphate will usually stop GSA. No nutrient, other than ammonia, is a cause of algae.
    That statement should be amended to read, "In a well-planted aquarium, phosphate is not a cause of algae."

    I spent part of last weekend fishing in a 25 acre lake that was over-fertilized with phosphates (and nitrates.) The transparency was about 6 inches. There were macrophytes present.

    Excess nutrients, mainly phosphates, are the reasons that many lakes and bays are dying.

    Bill

  6. #6
    We need to disconnect our aquarium "science" from the eutrophication issue in lakes and bays. The environments are totally different, the ecosystems are totally different, and it only confuses the issue to conflate them. By the way, I don't think it is established that ammonia is not the trigger for algae in lakes and bays. There are certainly many sources of ammonia present in such bodies of water. In any case we have so much difficulty disconnecting people from the belief that they have to minimiize phosphate in a planted tank that introducing irrelevant analogies isn't a good idea.

    Sorry, you pushed a hot button there!
    Hoppy

  7. Well, I will try increasing phosphate and see what happens! It will be a fun experiment if nothing else!

  8. #8
    Bill, when you have more than 30-50% of the entire surface area covered in a subtropical or tropical shallow lake with macrophytes, adding PO4 = more weeds, the lakes in Florida, 7800 are 4 hectarces or larger, are gin clear regardless of the PO4 content in the water column.

    You will get algae where the % of surface area is less, or where wind resuspenision or they have removed the plants etc occur.

    They have found no correlation between PO4 in lakes with macrophytes and algae.
    A good paper that refutes some of the older seminal work done by Philips 1978, was done at the old lab I worked at in UF.

    The number of lakes in the study far exceeds any other and addresses specifically the type of system we are interested in natural ecosystem, lots of plants, warm temps(no freezing), high % of coverage, shallow, fish, snails etc, and a wide range of nutrient levels from oligotrophic to hypereutrohpic.

    http://fishweb.ifas.ufl.edu/Faculty%...tics2004LR.pdf

    Take a long look at figure 1. You tell me if that figure has any high R^2 valve, eg, is PO4 correlated well with algae/plants etc?

    A similar figure appeared after adding the fraction of plants that Philips, 1978 left out(actually he just did not consider the fraction of PO4 locked up in the plants, but added the algae PO4 from the water column, that great skewed the results!).

    Removing such bias and parameters/methods that skewed things really makes is far less predictive.

    So we search for other parameters that are predictive, such as NH4.

    I have a non CO2 low light tank as well, if you think I've not added excess PO4, and I mean a lot, you would be mistaken, I've added 2-3ppm there, same thing with NO3, Fe etc.

    Never was able to induce algae if the system was well planted and doing well to start with.

    If the plants are hurting, or things are not that stable, then you can get algae.
    Try moving all the plants all around and see.

    That alone can easily do it, things happen slower in non CO2 planted tanks, the rate is slower for algae and plants.

    That's why I chose to use high light a long time ago to get a better understanding about algae. Took less time and was easier to see the relationships.

    If you do a large water change after moving the plants around, you do not get an algae bloom.

    As the article states, plants define the nutrients and the system, not the nutrients defining the plants.

    That realization has really been promoted in that group and they are very very sharp.

    So for low light tanks, high light tanks, CO2, excel, non CO2(but not marine planted tanks, the max range seems about 0.5ppm for PO4) etc, the excess PO4 is going to induce algae.

    If algae is already there, it may or may not depending on other issues.
    Still, if algae is there, then there are not enough plants, too much disturbance, poor conditions for the plants.

    This is the more technical paper:
    http://fishweb.ifas.ufl.edu/Faculty%...macrophyte.pdf

    Regards,
    Tom Barr

  9. #9
    Quote Originally Posted by VaughnH View Post
    We need to disconnect our aquarium "science" from the eutrophication issue in lakes and bays. The environments are totally different, the ecosystems are totally different, and it only confuses the issue to conflate them. By the way, I don't think it is established that ammonia is not the trigger for algae in lakes and bays. There are certainly many sources of ammonia present in such bodies of water. In any case we have so much difficulty disconnecting people from the belief that they have to minimiize phosphate in a planted tank that introducing irrelevant analogies isn't a good idea.

    Sorry, you pushed a hot button there!
    LOL - OK. The hot button is what keeps us young, I think

    My point was that the phrase "Excessive phosphates do not cause algae" applies to well planted aquariums and to natural bodies of water that have a lot of macrophytes. But in bodies of water that do not have a lot of plants, it certainly does cause algae blooms and contributes to their eutrophication. For example, here's a link to the home page of the Chesapeake Bay Foundation: Bay Stressors

    I believe that it is quite well established that excessive phosphates and nitrates are the main causes of algae in bodies of water that don't have a lot of higher plants.

    Not to be preachy, but it can be misleading to attempt to apply the principles that we have learned while growing plants in aquariums to the larger, natural world. It should probably work the other way.

    Bill

  10. #10
    Tom,

    Thanks for your reply.

    I agree that an environment with a lot of macrophytes will not develop algae from excessive nutrients.

    But I do think that one in which there are few plants will, or could, develop algae problems. That would explain the problems that we have in Chesapeake Bay and similar bodies of water.

    Bill

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