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Thread: How do live rock and susbtrate bind phosphates?

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    How do live rock and susbtrate bind phosphates?

    Hi,

    As per the title. I would like to know how the binding process takes place (via calcification of calcium phosphates?). Also, under what circumstances the phosphates bound in rocks and substrate get released (due to low pH?)? Finally, is it crucial to take into account of bound phosphates when calculating how much phosphate removal media to use?

    Thanks

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    Most of the binding that takes place is not between Ca++ and PO4- , yielding Calcium Phosphate but between Ca++ bound to CO3 - in carbonate minerals like Cacite, CaCO3. Here, lets say, in the Calcite or Aragonite, where allot of the Ca++ is exposed at the crystal lattice surface, the PO4 attaches to the Ca++ vis a Ionic bond, just like it attaches to CO3--. How much takes place is dependent on solution kinetics. In Seawater, the best binding takes place at a pH above 8.4.



    The addition of Kalk, also causes the precip of CaPO4 brought on by the very local pH, where the Kalk is added and brought on by the very high local pH where the Kalk is added and the reaction that takes place.


    2H3PO4[phosphate] + 3Ca(OH)2 [kalk]-------> Ca3(PO4)2 [calcium phosphate] + 6H2O

    Dissolution also is a function of solution kinetics, ie., Salinity, pH, temp, Alk, Ca++, etc. It is impossible to know where this is going to take place, only that low pH is a major dissolution factor and there is no real data at what pH that is but we can assume it will be in acid conditions. Calcium phosphate is much harder to dissolve that Calcium carbonate like Calcite or Aragonite. So, at least in pH water below 7.


    As far as GFO and its need to pick-up bound PO4, it can't remove it. Only free PO4 can be bound to GFO. As far as that bound PO4 and using GFO, in case said PO4 is released from the carbonate minerals, it is OK to use but don't bet on much bound PO4 is going to be released from carbonate minerals. Most phosphate issues are the guy in the mirror, not cleaning his/ her tank, over feeding, not paying attention to labels and how much phosphate they have. Most phosphate issues are not from PO4 but from organic phosphates, which your kit can not measure, unless you have the full blown phosphate kit from HACH, for $ 150.

    Lastly, once LR or carbonate minerals become coated with organics and/ or bacteria the are very poor at PO4 removal, although there may be a wee tad that still gets bond to the carbonate minerals through diffusion. But here too, like clean fresh surfaces, equilibrium will be reached and any further binding will cease.
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    Thanks Boomer.

    What breaks up the ionic bond between Ca++ and PO4?

    Is it always a good idea to use extra phosphate removal media over and above recommended levels by the manufacturer of a GFO media in case there are some bound phosphates?

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    See edit repost repost, I was having some issues.
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    Thanks again for your very informative reply.

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    What breaks up the ionic bond between Ca++ and PO4


    Dissolution by low pH, which will also be some what dependent on pH, Alk and Ca++.
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    Boomer, seems to me like you might be able to answer this question. It's been posed in this thread http://www.reeffrontiers.com/threads...570#post707570 and about 50 other across the net that you can cause the release of bound phosphate. Regardless of the method of filtration, I'm interested in a more detailed explanation of why or why not this is possible.

    Because there definitely is an abundance of anecdotal evidence to suggest that this theory, clearly stated on post #144 of that thread "Phosphate flow out of rocks", does happen though the explanation given is vastly over simplified.

    I'm interested in an actual explanation of what really is or could be happening. I haven't been able to lock in on one particular explanation outside of some kind of relationship between bacteria and algae working together to cleave bound phosphate out of the surface of the rock.

    For reference, a lot of people (who have typically neglected their tanks to some degree) find that after adding an algae scrubber and getting N and P under control, algae grows from the rocks (sometimes in tanks that had no algae problems prior) for a period of time, then this algae will wither away and die and the tank will then remain algae free. This sometimes takes months to a even a year on a severely neglected tank. Some claim to even be able to repeat it by removing filtration and even adding phosphate to saturate the rocks, then adding filtration back in to 'suck it out'.

    I look forward to your input on this subject

    Thanks
    Bud

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    Boomer, may I please ask a question, and let me start by saying I don't have an in depth understanding of reef chemistry, I know enough to keep my corals growing and my tank looking good, but the actual science behind what is occurring is something I unfortunately don't have time to figure out. In other words, I understand adding GFO reactor can lower my P04 or that turning lights off at night causes PH to drop, but I don't understand why, and to be honest, I don't have the time to learn. I do however have a practical question I was hoping you could answer for me.

    I have always been concerned with phosphates since starting my earliest tanks I always see a green hair algae bloom early in the cycle and have been told by LFS, Boards, et all. that this is because my new base rock was leeching phosphate. I have also been told that white PVC pipe we all use in our plumbing, and the white eggcrate I use under my sand bed leeches phosphate. My phosphate levels are currently next to nill, and a few months back i was considering buying a GFO reactor from OBD a local sponsor. But i was told by Becca that it was pointless, that once my tank is established the pipes and rock will no longer leech phosphate so if i have good RODI source make up water then there is no reason to add GFO to a system that doesn't appear to have a current phosphate issue.
    Is this true? Does rock and white pvc, white egg crate leech for a certain amount of time, then stop leeching and no longer cause an issue?
    Here is the same question and response from another forum, they are basically asking the same thing i think.
    OP will older live rock ever STOP leaching P04??
    Reply Yep, once it's leached it all out. There is only so much PO4 that it can contain. Usually cooking rock for a month or two (sometimes longer) will get rid of most if not all of it. A quicker method is giving them a bath in a water/hydrochloric acid solution. Burns every last bit of phosphates out of them, but you've got to rinse the rocks REALLY well several times afterward.

    thanks for your time Boomer.
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    Is this true? Does rock and white pvc, white egg crate leech for a certain amount of time, then stop leeching and no longer cause
    Yes, pretty much it. Many PVC use phosphate plasticizers. Basically those P at the very surface that may leech.



    There is only so much PO4 that it Burns every last bit of phosphates out of them, but you've got to rinse the rocks REALLY well several times afterward.
    There is no such thing as burring out all bound PO4. PO4 is found through out the Aragonite put there during coral formation. Rock is quite porous and most of that PO4 is not bound. There is no proof what so ever that a acid bath is better than over night 100 % bleach.
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    Quote Originally Posted by Boomer View Post
    There is no such thing as burring out all bound PO4. PO4 is found through out the Aragonite put there during coral formation. Rock is quite porous and most of that PO4 is not bound. There is no proof what so ever that a acid bath is better than over night 100 % bleach.
    But bleach is a base, vs muriatic which is acid. The acid will dissolve the rock, so it is my understanding that 20 minutes is all you really need or should do in acid. Bleach you can do all night because it doesn't dissolve the rock - it just kills everything and leave the rock matrix in tact. Right?

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    And what happens when you dissolve rock with an acid. It for all practical purposes is melting the rock, closes pore, locking in things in some of those pores. At the same time the rock, made of calcium carbonate that is dissolving, releases CO3--, which a base, which raise the local pH, Alk, causing the re-precipitation of the calcium carbonate and the re-precipitation of Calcium phoshate which you are trying to remove allot of it gong right back to that rock. Now you have a more fresh new surface, which does what when you put it back in the tank. Causes the immediate precip of Hi-Magnesium Calcite on the rock surface and precip of Calcium phosphate. And your rock is going right back to where you were.

    Still waiting for anyone to explain how algae is removing chemically bound P for a rock.
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    So a muratic acid bath is a waste of materials and time?

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    Interesting. I am in the process of bleaching rock now, almost acid bathed. Being winter I went the route I could do I side though.

    The way I understood it the P was locked in the outer layer and was ate away by the acid leaving a clean porous rock when done. It sounds like you are saying the acid eats the P and some of the rock ONLY to reveal a new layer still filled with P. Bleach will at least clean the rock, though not affecting the P level.

    Starting with bleached rock in a new tank, would you recommend GFO straight off the bat? Normal recommended amounts or possibly double?

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    Goby
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    Quote Originally Posted by mfinn View Post
    So a muratic acid bath is a waste of materials and time?
    Not only a waste of time, but when it comes to phosphate. It appears from what he is sayi g that it is actually counterproductive. Interesting.
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    Surgeonfish
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    Quote Originally Posted by Ichthys View Post
    Not only a waste of time, but when it comes to phosphate. It appears from what he is sayi g that it is actually counterproductive. Interesting.

    I can only relate what I've read in threads where Randy Homes Farley has posted on this subject, and he seems to think that it is beneficial.

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