Aquarium Chemistry Question? Ask the Doctor!

Discussion in 'Reef Chemistry by Randy Holmes-Farley' started by revhtree, Mar 22, 2016.

  1. Sgchick

    Sgchick Member

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    Hi Randy, I just bought a new Salifert Alkalinity test kit and noticed the directions have changed. The old kit said to add 4 drops to your tank water (4ml) and 2 drops for low resolution. The new kit says to add 2 drops and (1 drop) for low resolution. Did I get some bad instructions? Not sure how to find out ...Thanks, Melanie
     

  2. Scott.h

    Scott.h Valuable Member Build Thread Contributor

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    Referring to the ph, what makes 7.8 concidered to be the low point? What is happening at 7.7 or below to make coral skeletons dissolve? The lower the ph does that make the oxygen levels lower in the water as well?
     
  3. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    pH is independent of O2.

    The exact pH at which calcium carbonate is exactly saturated (dissolves at lower pH, precipitates at higher pH) depends on the alkalinity (the carbonate concentration, specifically) and the calcium level. Higher alk (carbonate) and higher calcium raise the saturation pH.

    A doubling of either (alk from 7 to 14 dKH or calcium from 420 to 840 ppm) will move the pH of saturation up by 0.3 pH units. It also depends a little bit on temp and salinity (and even pressure in the very deep ocean).

    geeky math below.... :D

    The saturation state is actually determined by:

    (2) Ksp* = [Ca++] x [CO3--] (saturation)
    (3) Ksp* < [Ca++] x [CO3--] (supersaturation)
    (4) Ksp* > [Ca++] x [CO3--] (undersaturation)
    where Ksp* has an exact, known value, [Ca++] is the calcium concentration, and [CO3--] is the carbonate concentration

    this is discussed more here:
    Chemistry and the Aquarium: Calcium ? Advanced Aquarist | Aquarist Magazine and Blog
    http://www.advancedaquarist.com/2002/3/chemistry

    In exactly normal NSW at about pH 8.2, the water is slightly supersaturated by a factor of about 3 relative to aragonite dissolution and precipitation. That is, the product [Ca++] x [CO3--] is 3* the Ksp*

    Each drop in pH of 0.3 pH units corresponds to a decrease in carbonate concentration by about half (as it is converted into bicarbonate). So a drop of 0.3 pH units is a drop in carbonate by half, and hence a reduction in saturation/supersaturation by half. A drop of 0.6 pH untis is two drops by hal, or a drop to 25% of the previous carbonate level.

    In order to lower the supersaturation (Ksp*) to exactly 1 from 3 (meaning it is exactly at its solubility limit), a pH drop of about 0.48 pH units is required. That drop lowers the carbonate by about a factor of 3.

    So a drop of 0.47 pH units from a starting point of 8.2 gives us a pH of about 7.7. :)
     
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  4. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    The amount of colorant added is not important to the test, as long as you can distinguish the colors. :)
     
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  5. Sgchick

    Sgchick Member

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    Perfect!! Thanks Randy!
     
  6. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    You're welcome.

    Happy reefing. :)
     
  7. Scott.h

    Scott.h Valuable Member Build Thread Contributor

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    What would be the difference in worrying about bacteria in RO/DI vs someone that has a well pumping water out of the ground? There are no chemicals in well water to prevent bacteria growth. We don't clean out/sterilize pipes in our house. Wouldn't that be the same scenario?
     
  8. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    Probably. Well issues might be worse since it might be a friendlier environment to bacteria than the really low ionic strength RO/DI.
     
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  9. zieg9479

    zieg9479 Active Member

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    Randy, Any idea what's going on here?
    A few months ago I threw in a bag of API activated carbon. I hadn't tried it before and wanted to see if it would benefit my tank. Well, I couldn't decipher a difference but I had also forgotten about the bag in the sump.
    I also run n/p pellets and decided to look at that today. I saw I had a bag of carbon in there and pulled it open knowing it was likely spent and full of DOCs.

    Anyway for those curious here is the visual result. There is the original carbon, and smaller brown, rusty particles. I have no idea what the orange roe looking pellets are. The casing is hard but they can be smushed. The only livestock I have down there is an emerald crab, macroalgae, and hitchhiker porcelain crabs.
    Are the casings DOCs and why do I see what looks like rust from activated carbon (It smeared like rust)? Impurities? Does this mean I am getting some GFO-like benefit?
    [​IMG]
     
  10. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    You never used any GFO? It looks to me like a mix of GFO and GAC, plus the round beads of undetermined nature.

    Do you recall the exact API product? They have some that are mixtures of activated carbon and other things (e.g., AMMO-CARB)

    The beads might be a DI resin?

    Overall, the mix of things looks possibly like ChemiPure Elite, which has GAC, GFO, and DI resin all together. Any chance you used that?
     
  11. zieg9479

    zieg9479 Active Member

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    hmm maybe I did have chemi pure in my sump...
     
  12. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    If possible, that's the most likely explanation. :)
     
  13. Danny Venditti

    Danny Venditti Active Member Build Thread Contributor

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    Randy,

    I switched from Aquaforest 1,2,3, to B-Ionic 2 part. Will it be necessary to dose extra Mg to maintain the level at 1350 or does the 2 part contain enough?
     
  14. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    B-ionic should maintain it, at least for a substantial period. I'm not sure how much consumption of Mg they assumed.
     
  15. Danny Venditti

    Danny Venditti Active Member Build Thread Contributor

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    I bought a bottle of ESV Mag anyway just in case but haven't used it yet.

    Also what would cause Ca to remain the same over several days with no dose. Corals seem fine but Ca has not moved at all for 4 days?
     
  16. Danny Venditti

    Danny Venditti Active Member Build Thread Contributor

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    Mg @ 1350 and ALK is 8.3
     
  17. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    How much did alk decline?

    If you lost 1 dKH per day, you might hardly see the calcium decline, since it is only about 6-7 ppm per day.
     
  18. Danny Venditti

    Danny Venditti Active Member Build Thread Contributor

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    ok that makes sense. The DKH was 8.0 and I am slowly bringing it up after a 15% water change (Tin came up on recent test) I think it just probably needs time to adjust to the change and new dosing.
     
  19. Danny Venditti

    Danny Venditti Active Member Build Thread Contributor

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    so Randy, what is your opinion on dosing frequency

    1. A little several times a day
    2. More each time and less times a day but spread out.
    3. Same as 2 but close together
    4. all at once and only once a day
    5. it doesn't matter/
     
  20. chomoney

    chomoney Active Member

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    Randy -

    What are the potential downfalls are high potassium levels in a reef tank? Also, if there are negative effects, what level would you consider “too high?”

    Thanks!
     
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