Calcium - Alkalinity - pH

bang guy


Originally posted by slowest is fastest
Good thread.... I disagree with the notion that adding just calcium is unwise and will mess up alkalinity though.

You can disagree, but it is definately true that if you only add Ca it will mess up ALK and Mg. Your Ca will rise faster than the ALK and precipitate. This will have the net effect of diminishing Ca and Mg levels.
When a Coral uses a Calcium ion it will require two Carbonate ions to form Calcium Carbonate. If you only add Calcium, then where will all the carbonate come from?? Many people make the mistake of thinking Corals build Calcium skeletons. This is far from the truth. They build Calcium carbonate skeletons.
Broomer is right on with his statements, there is plenty of analysis that has been completed backing up his statements.


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God damn broomer, I've gone crosseyed trying to decipher all the technical information...still trying to interpret that equation :p
Nonetheless, it really helped to shed the light on why such levels go where they go, I'm definately going to start testing more then what I do. Thanks for the post, and it should definately be archived for future inquires because it don't get much better then that.

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OK i was the one that started this post and now i am more lost i want to my lfs today and this a$$hole (from what you guys are tell me he is) that my calcium will be ok that alkailinty is when your ph is high and my ph is like 8.2-8.3 he was tring to sell me a ph test kit. So is there a alkaility test kit. This is what i am testing for wright now ph-8.2 to 8.3 nitrite-0 ammonia-0 copper-0 calcium-600 (just did the test) what are the other thing i need to test. I am going to take some water to my lfs tomorrow and have them test it and see what they get. What do you all think of Hagen test kits?????


I have trouble understanding the applicability of the equation...
CH3-CH2-OH + O2 ----> Acetic acid + water
That equation starts with ethanol! and everybody knows that ethanol will not react with oxygen to produce vinegar under ordinary circumstances. That equation simply does not apply to the situation at hand. That situation can happen in the laboratory, under intense heating and with the help of a strong acid like HCl to catalyze that reaction, you have to remember that the bonds involved in the equations are covalent bonds and as such, are very difficult to break without heat and a catalyst (in this case a very strong acid, HCl)...both of which do not exist in our tanks.
The inverse relationship with calcium and alkalinity is due to the fact that an alkaline solution will precipitate the Ca in solution making it less available.
Ca (aq) + HCO3 (sol)

> CaCO3 (precipitate) + H2O
The low pH drives the above equation to the left. Keeping more Ca ions in solution.


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Thanks for pointing that out Rockster.
I mearly inserted a pic detailing acetic acid, not meaning to include anything left of the arrow, nor the water molecule.
Basically was just inserting a pic.
There was no reference to ethanol, nor was it my intent to even include this part of the formula for acetic acid.
My bad.
I've corrected it.
Thank you
And regarding your words
That equation starts with ethanol! and everybody knows that ethanol will not react with oxygen to produce vinegar under ordinary circumstances.
Just to mention - I didn't know that ethanol will not react with oxygen to produce vinegar. I am not a chemist, and it's been years since I studied it.
Therefore ...... everyone doesn't know that.


hmmm, I'm dizzy!!! :eek: And I thought the books where confusing me...ROTF
In all seriousness — thank you so much for this conversation! It was been a great help. I noticed a tread about an algee problem a couple of weeks ago and it was suggested that the ALK be tested. Guess what I wasn't testing and guess what problem I was having...Yep, your first two don't count.
Well, ALK was low, Cal was high. Didn't take long to solve the algee problem.
I'm wondering if anyone knows of any software that is designed to store the readings and chart them for us. I've always found a visual tool helps to show relationships. (Not that my ex-wifes ever noticed...LOL) I know some of the computers have the feature and I plan on using one of them. But in the mean time I'd like to use some software!!
Let's see here — where did the print screen go??? LOL
Thanks again!
Ok broomer im sticking this one to you because no one knows whats going on. My Ph is high 8.6. I cant get the calcium above 300-350 ppm and my alk is high. I did a 50% water change today and the PH is the same. What should I do. Im so lost lol


Read this: I had the same prob until I added Kent Marine Tech-M, a magnesium supplement.
Originally posted by broomer5
slowest is fastest
By all means ... No offense taken and I know no harm was intended.
You make a very good point - one that has also kept me wondering. That is, what is the role that magnesium plays in our tank and waterchange water - and how does it come into play.
I believe I understand that having insufficient magnesium, less than the 1300 ppm found naturally - can prevent us from keeping our calcium levels up into the 400ppm+ range.
This I've read before - but have little direct experience.
My statement that adding just calcium will mess up your alkalinity - is true if, and only if, everything else is somewhat constant, stable and holding at a known level. I believe that this includes magnesium too.
I try to avoid using the phrase "all things being equal" that we've read so often. IMO - this phrase is one of the most dangerous presumptions we can make - because as you know - nothing is equal and everything changes in the tankwater - given enough time and load.
Your's is such a great case to mention - because it shows how a change in one - changes another. In your case - a significant drop in magnesium, allowed your calcium level to max out down around 300 - even with the reactor running. The lower magnesium level "prevented" the calcium from being saturated up in the 400+ range.
Another piece of the puzzle.
Were you able to determine what the loss of magnesium was due to ?
Did you change saltmixes or do a substantial water change, or anything else out of the ordinary, or do you think that the drop in magnesium was or is a natural occurance in our tanks ?
I'm always eager to hear of other's experiences such as yours, especially on this topic. It interests me. I certainly don't have all the answers - and like many - I am trying to learn too.
Helps us to figure it out on our own tanks - on a friendly, accessible level.


Active Member
Please explain BigMac
I would like to hear why this is true - as I said before - I am trying to learn and would appreciate any thoughts you might have.
I do not run a calcium reactor, although I think I understand how they work.
Could you offer up some more details ?


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yes bm, please elaborate. i too am a little confused by your statement. if you are running a calcium reactor, and adding kalk, then you can throw all this out if you are testign properly. i have a ca reactor on my 135 adn drip kalk, and my bioload is gigantic, but i have no problems with ca, alk, ph.
good luck
First precipitation of calcium carbonate is often stopped(even at supersaturation levels) by several things happening in our tanks. Mg and organic molecules play a big role. Try here for specifics "Captive Seawater Fishes" by Stephen Spotte (1992).
Instead of doing what I am sure would be a long confusing and probably incorrect job of explaining where the "extra" carbonate might be found I will humbly suggest the following article. Perhaps it also says what others are already stating and I just do not understand. In either case it address all points of Calcium and Alkalinity and may even provide some with new information.
If posting the link is not permitted than I apologize in advance.
PS BangGuy...I am glad we can agree to disagree :D


con someone answer this one to me. Why when the lights are on that the PH goes up and does this happen only with MH's or also VHO's and NO Flor and PC's ....just wanting to know


Active Member
Thanks BigMac !
I think I understand.
Since you are dissolving the reactor media, you are basically adding both calcium AND carbonates together.
If you run it lower you are adding LESS calcium and carbonates together ........
Therfore both your levels follow each other.
Calcium drops and carbonate alkalinity drops - because you are running the reactor at a lower rate - and not adding calcium or carboantes near what you do when your run the reactor at a higher rate.
If this is your experience - it makes sense to me.
Sort of like getting things lined out dosing a 2-part additive say at 25 milliliters of Part A and part B. each time you dose. Everything looks good - and levels are good.
Then reducing that dose to say 10 milliliters of part A and part B, but staying on the same dosing schedule.
The tank continues to use the calcium and carbonate up at a somewhat constant rate - determined by the load demands - but since you are adding LESS of each component - both the calcium and alkalkinity drops.
I hope that's right ????
If not - please correct me.
Side note:
This thread was started for just this type of discussion. Nothing more than to open up a topic that can be confusing at best - and difficult for most - myself included.
I don't want to become a number chaser - fiddling around with water chemistry anymore than the next guy.
But I do want to make a point that when we talk about this stuff - that it's more than just one additive, one supplement or one thing that could be the root cause.
It's a lot of things going on at once - that makes it tricky.
Knowing it "all" is impossible.
Knowing "some" is fairly reachable if we work at it.
Knowling "very little" makes it tough when things go wrong.
Knowing "nothing" - makes it so hard sometimes - when it doesn't have to be that way. But we all knew nothing at one point.
I think MOST of us would be happy to just know "SOME" to a point where we understand what's happening in our reef tanks.
Leaving the rest to the "guru's" and folks that write such wonderful articles for us to read.

bang guy


Originally posted by slowest is fastest
PS BangGuy...I am glad we can agree to disagree :D

Absolutely! :) I don't know any experienced reefers that have not had one of their understanding completely turned upside down. I was ready for such an event with your post. However, I'm still missing the understanding of where you believe your Carbonate is coming from to replace what was used during Calcification. So, I am forced to adhere to my belief that only adding Calcium without a corresponding Carbonate or buffer dose will cause an imbalance.
In fact, after rereading your first post, I believe you had a precipitation event that caused your Ca and Mg to fall dramatically. This is the primary symptom of unbalanced Ca/ALK levels. Your post actually strengthened my belief that dosing only Ca will cause an imbalance.
PS. Thank you for the link. Randy is, in my eyes, one of the premier Reef chemists in the US, if not in the world.
When the lights are on and photosynthesis is occuring, carbon dioxide is taken up, oxygen is given off and PH rises. When the lights are off, photosynthesis stops Co2 rises and PH falls
All I can say is yep...uh huh...yep...ditto :D :D :D
Nothing is ever as simple as it seems on the surface or as simple as we would like it to be thank goodness some people do understand and are willing to write about it though ;)
The reactor has been up and running for almost two years. With the exception of adding extra calcium to the system in the begining to raise it to 450-460ppm I had not made additions of any extra calcium. My reactor has (had) kept everything where I wanted it until the "incident" With the huge change in colors (not bleaching) and the subsequent growth spurt I noticed I was inclined to think (perhaps incorrectly) that a huge uptake had occured not precipitation...I may of been wrong. Since then all but the button polys have returned to their normal colors and seemingly nothing else has happened.
I sure hope all that calcium I added to raise the levels back up after the incident won't bring things crashing back down (crosses fingers lol) so far so good though :)
PS I agree Randy is definately one of (if not) the best!

bang guy


Originally posted by slowest is fastest
The reactor has been up and running for almost two years.

Ahhh, mystery solved. I somehow missed that you are using a reactor. Ca reactors add Calcium and Carbonate/Bicarbonate in a balanced combination (1:2). That's your Carbonate source. I misunderstood completely.
I had thought from your post that you were adding Calcium chloride or some other "Calcium only" source. That is what Broomer was alluding to in his post, and the reson for my retort. I think this was an extremely informative thread and I hope it's archived in some way.


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i dont understand. is this an important thing for fish only tanks or reef tanks? i hate science. can someone post the ranges that all these things should be.