How much kalkwasser can a tank take?

Discussion in 'Reef Chemistry' started by HiFidelity, Dec 16, 2014.

  1. HiFidelity

    HiFidelity Guest

    Hi, I've got some curiosities about the limits of kalkwasser.

    Currently I'm dosing a cocktail of 45ml vinegar/3 spoons kalk/1 gal RO water. Only when lights are off.
    Previously I simply dumped 2 spoons of kalk in my 5 gal bucket of ATO water.

    So now I'm keeping a personal record high of corals in my tank and finally my coral consumption is high, my ALK is stuck at 7, ph 8.25-8.45, Calcium down to 400 and this is the first time my calcium is actually dropping even with the dosing of kalkwasser.

    I want to push my kalk to it's very limits before I begin to dose 2 part or any other method than what I'm doing now so I got to wondering, how much kalkwasser's too much?

    I was thinking what if;

    A. I stopped super saturating my controlled dosing of kalkwasser so basically back to 2 spoon/gal & no vinegar but in addition put the vinegar in the ATO along with 2 spoons kalk/5gal of ATO water, can this yield any adverse side effects? I can not simply add kalk to the ATO without vinegar by the way because my PH can max out at 8.5 when the lights are on.

    B. Switch from 1 gal dosing container of super saturated kalkwasser to 2 or 5 gal and increase the current dose.

    Which would you go with or neither and why?
  2. sfsuphysics

    sfsuphysics Supporting Member

    Have you tested the pH of your super saturated kalk? Presumably that's the magic number that you're trying to avoid. I mean the vinegar takes it down a notch or two doesn't it? How are you dosing it btw? hopefully not all at once.

    Unfortunately increase the dosing amount with more volume of water means that you need to evaporate that much water anyways, which I'm not sure if you're actually losing that much water.

    What I would do is 1) test the pH of your vinegar/kalk mixture. 2) if the pH isn't too high, increase the kalk, leaving the volume of water the same, 3) slowly drip it (peristaltic pump) and keep monitoring your pH. Changing your pH long term is incredibly difficult to do. 4) If you're still having problems, add baking soda & calcium chloride (separately) to your dosing regime.
  3. bluprntguy

    bluprntguy Webmaster

  4. HiFidelity

    HiFidelity Guest

    no issue with PH, after several seasoned reefers said it's good and after I noticed that all the corals seem to love the PH closer to 8.5 I'm no longer considering that an issue, perhaps 7 dkh isn't bad either but my peppermint shrimp all disappeared in a rather short period of time so I'm leaning towards raising the alk a little bit. Even if the shrimp die off isn't an issue it still makes me nervous to be on the bottom end of the alk range, no room for error there if say I forget to refill my kalk container or something like that.

    My current kalkwasser dosing regiment does not increase PH, when the lights are on kalkwasser stops, the fuge light is off and PH is a solid 8.4-8.5, once the lights shut off kalkwasser is dosed once every 10 min and fuge light kicks on, PH still drops to about 8.25.

    I guess to clarify my question, do I increase my current dosing regiment (only at night) or start dosing day & night with vinegar during the day and no vinegar at night in hopes that i could hold a higher PH value during the night and also bring overall ALK slightly higher? considering that my vinegar spiked kalkwasser and slow dose seems to have absolutely no effect on PH!

    By the way at 45ml vinegar & 3 spoons kalk/gal the mixture is always milky, never clears up. Thanks for the article, that page is 90% of the reason why I'm running kalkwasser all together :)
    Last edited: Dec 16, 2014
  5. sfsuphysics

    sfsuphysics Supporting Member

    The only issue I could see with adding more vinegar is the carbon dosing you're doing as a result, could get bacterial blooms.

    Do you have a monitor that keeps track of the pH like Apex or other controller? I'd just increase the kalk mixture and see if that has any adverse effects, or increase the total amount that you dose, presumably you don't dose 1 gallon per day?
  6. HiFidelity

    HiFidelity Guest

    Not 1 gallon per day, more like 1 gallon super saturated kalkwasser every 5-6 days.

    Sorry I know it sounded confusing in the first post but I'll try to clear it up haha...

    I am currently dosing super saturated kalkwasser (3 spoons/gal) that is also spiked with vinegar, I've been doing it for a while. The vinegar is there so I can get the 3rd spoon of lime to go into solution. I've been dosing this way for almost a year and always only on at night.

    Now I want more Alk & would like to see PH higher at night (nit picking), should I start dosing more than 1 gal/5-6 days of supersaturated kalkwasser? or should I go back to the normal 2spoon/gal kalkwasser mix at night and put the same dose of vinegar in ATO along with some lime? (amount adjusted as needed without raising PH over 8.5) Vinegar would keep the lime in the ATO in check and the ATO wouldn't get the full 2spoon/gal but instead a fraction of it and then increase till tank demand is met.

    Basically 2 ways to skin this cat, which one gets me where I need to be? which is a little more Alk & slightly higher PH at night, the later not absolutely necessary but I figure it doesn't hurt to smooth out the PH curve from night to day.

    One way or another I need more kalkwasser dosed, Alk & Ca have both been on a slow but steady decline, almost proportional to the amount of coral growth/addition.

    I have a controller, PH is monitored in real time, probe calibrated regularly.
    Last edited: Dec 16, 2014
  7. bluprntguy

    bluprntguy Webmaster

    Seems like you could dose more kalkwasser overnight. Maybe extend the time you are dosing by an hour? If you are using the kalkwasser to help even out your PH swings, then you just shouldn't be dosing during the 6 hours or so that your lights are on high.

    I dose my tank with kalkwasser through the ATO, so my 26 gallon system runs through about 3 gallons of super saturated kalkwasser in about two weeks.
  8. HiFidelity

    HiFidelity Guest

    do you use vinegar to make super saturated kalkwasser?
  9. bluprntguy

    bluprntguy Webmaster

    Yup. I use like 1/2 cup per 3'ish gallons.
  10. HiFidelity

    HiFidelity Guest

    Would you say 2 spoon kalk/gallon & no vinegar would raise PH more than 3 spoon kalk/gallon with vinegar?

    I get the feeling that the vinegar in my kalkwasser is stopping it from raising PH at night, I've tried doubling my dose for a couple of nights and PH remained the same which is what got me thinking about dosing around the clock; during the day with vinegar and at night without...
  11. bluprntguy

    bluprntguy Webmaster

    Only way to find out for sure is to check the PH of your kalkwasser somehow or experiment on your tank. I would think that the the relatively minor amount of vinegar that you are adding to your kalkwasser solution probably isn't lowering the PH that much, if at all.

    Actually, you could do the math: PH of vinegar is 3.0; PH of Kalkwasser is 12. You are adding 45 mL(.0118 gallons) of vinegar to your gallon of kalkwasser. The vinegar changes the PH of the Kalkwasser from 12 to 11.96.

    If you are putting in two TEASPOONS of kalk per gallon you aren't really supersaturating your solution. You need to add more kalk. Otherwise the vinegar won't really do anything because there isn't more kalk to saturate into the solution.
    HiFidelity likes this.
  12. HiFidelity

    HiFidelity Guest

    thank you for providing a more logical perspective haha I was starting to get carried away with my not so scientific approach, I'll try more kalk at night & see where things go...
  13. sfsuphysics

    sfsuphysics Supporting Member

    Can you do the math please? I don't know much about chemistry other than the pH scale is logarithmic, so doing a weighed average of one pH vs another doesn't work. It seems that might be what you did, but maybe it just came out close to that?
  14. bluprntguy

    bluprntguy Webmaster

    Maybe I should say that the excel document that I downloaded from the internet did the math for me, but it did seem like a reasonable answer...
  15. HiFidelity

    HiFidelity Guest

    would happen to be able to share that doc? :D
  16. bluprntguy

    bluprntguy Webmaster

    Urgh, I didn't save it. If can locate it in my history I'll post it.
  17. sfsuphysics

    sfsuphysics Supporting Member

    Gotcha, I'm not saying it's an unreasonable answer. However when I took a weighted average of pH with respect to volume I got an answer close to that 11.89 instead of 11.96... it could be that with such a small amount of vinegar that is that close to a weighted average. I've tried to read a few things online on how to do it and I'm not quite sure I get it... damn chemists they make things too difficult! :D
  18. bluprntguy

    bluprntguy Webmaster

    LOL. I hated chemistry, so I'll trust your answer way more than mine. Regardless, it's a fairly insignificant reduction from the vinegar.
  19. sfsuphysics

    sfsuphysics Supporting Member

    No no, I don't trust my answer at all that's the point, the fact that my answer I don't trust was so close to yours is what made me question yours :D
  20. gaberosenfield

    gaberosenfield Juvenile Chromis over an Acro in the Red Sea

    Ok, I'm going to attempt to actually do the math here. I need a refresher on my acid-base chemistry anyway, so take my calculations with a grain of salt :p

    Starting with saturated CaOH = 1.73 g/L at 20 celcius (from wikipedia).
    1.73 g CaOH/L * 1 mole CaOH/74.093 g CaOH = 0.023 moles CaOH/L.
    1 gallon = 3.8 L, so you have 0.089 moles CaOH in your gallon of saturated kalkwasser.
    This equates to 0.089 moles OH-/3.8L = 0.023 M OH- (just as I calculated above!). pOH = -log[OH-] = -log(0.023) = 1.64.
    pH + pOH = 14 (a definition given by the dissociation constant of water), so 14 - pOH = pH = 14 - 1.64 = 12.36. So saturated CaOH solution should have a pH of approximately 12.36.

    Now to tackle the 45 mL of vinegar. According to wikipedia, vinegar is typically between 3 and 9% acetic acid by volume. We'll choose 5% as a nice midpoint. So 5% of 45 = 2.25 mL acetic acid. Acetic acid weighs 1.049 g/mL (wikipedia), so 2.25 * 1.049 = 2.36 g acetic acid.
    2.36 g acetic acid * 1 mole acetic acid/60.05 g acetic acid = 0.039 moles acetic acid in 45 mL vinegar.

    Now you mix the two. One mole of vinegar should neutralize one mole of OH- generated by the CaOH in water.
    So 0.089 moles OH- - 0.039 moles acetic acid = 0.05 moles OH- + 0.039 moles acetate- + 0.039 moles water (plus all the other water in which this is all happening) in 3.845 L (3.8L starting solution + 45 mL vinegar). So thats 0.013 moles/L OH- and 0.01 moles/L acetate-.

    Calculating the pH of a 0.013 M solution of OH- is trivial:
    pOH = -log[OH-] = -log(0.013) = 1.89
    pH + pOH = 14, so 14 - pOH = pH = 14 - 1.89 = 12.11.

    The hard part is calculating the contribution to pH of 0.01 M acetate-. I am not sure how to do this because all the equations I've tried to use end up forcing me to divide by 0 (a sure sign you are messing up in any equation because the result is undefined!). However, I will wager a guess and say that the contribution to pH of the acetate should be negligible because acetate- is much worse at grabbing protons out of solutions than OH-. Thus, I would expect the pH of your mix of kalkwasser and vinegar to be approximately 12.11, or maybe very slightly higher.

    One important note: although the acetate- in the kalkwasser solution probably won't contribute much to the pH of that solution, once the acetate- enters your tank where the pH is closer to 8 it will act as a base and add extra alkalinity to your tank. Thus, although the pH of your kalkwasser + vinegar solution isn't much different from your regular kalkwasser solution, it probably adds significantly more alkalinity to your tank. Also, this calculation does not factor in that you are adding an extra amount of CaOH to your kalkwasser + vinegar solution! This is only for taking a regular solution of kalkwasser and adding vinegar to it.

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