Ca and Alk Balance

[erikharrison]

Could someone explain to me the CA and Alk balance scenario and how it would apply to reefing? I see on sites varied readings and I am confuzzled. :)

[Texreefer]

Eric ,
start here.. this gives some good info


oops,, here is the link
http://www.maast.org/forums/showthread.php?t=38345

[hobogato]

gonna give an example i heard from garyp and richard at different times, not sure who it originally came from.

think of a jar of red (alk) and blue (calc) marbles. only a certain # of marbles can fit in before the jar overflows and they fall out.

same thing with alk (ability of the water to buffer the pH by way of carbonate concentrations) and calcium (in ppm) concentration. only so much can "fit" in the water with out over flowing (precipitation) NSW is about 410 ppm calcium and around 8 dKh. that is in balance. if one goes up, the other goes down (bad) or there is precipitation and then they both go down (very bad).

that balance can be attained/maintained various ways, including chemical additives and reactors. both calcium and carbonate (alkalinity) will tend to drop over time as the corals use them up to build their skeletons and must be replaced.

this simple answer doesnt even touch other concentrations like magnesium and borate which can alter alkalinity and calcium concentrations.

are you more confused now? :D

[erikharrison]

7-15-2007:



Ca



Mg



S.G.



Alk


Value

520

1500

1.025

11.8


The above is an example from invinicible's blog, I was confused since most people keep their CA around 440. I was trying to figure out the relation between the two. The link you sent me told that it was important to keep them in check, but no explanation as to why.?.? I am trying to grasp reef chemistry, and it's hard for me since I am a high school dropout! :P

[erikharrison]

Ace, we were posting at the same time, thanks for the layman's example. I did have a feeling that if one was out of whack some precipitation would occur. I have so gotten lost on invincible's blog, it is great. :) I am sponging as much as possible!

[matt]

It's not quite the see-saw example that's implied by some. For example, if your Ca is 350PPM and your Alk is 9dkh, and you add 50PPm Ca to bring it to 400, your alk will not drop due to the increased Ca. But, Eventualy as you add either Ca or carbonate, you will reach over-saturation on one of those and you'll get some precipitation, which will quickly lower both Ca and Alk.

In terms of normal dropping of Ca and Alk due to calcification, I believe the ratio is 20PPM of Ca to 1dkh of Alk. Alk will drop "faster" than Ca because as a percentage of total Alk, 1 dkh is about twice as high as 20PPM of Ca is of total Ca. Make sense? If your tank uses 1dkh of Alk every day (like mine), it means you're dropping about 10% of your total Alk daily, as it's normally measured. 20PPM of Ca is only about 5% of total Ca.

The solubility of Ca and carbonate in sea water is ph dependent; that's why Calcium reactors work at such a low ph. The higher your ph, the lower your solubility. This can become an issue if you're using KW and b-ionic (both high ph supplements) and attempting to keep a very high Ca and/or Alk level.

A really easy way to keep your levels in balance is to initially get the levels where you want them using something like Calcium chloride and baking soda, then ONLY using "balanced" supplements like KW, both parts of a 2 part system, and/or a calcium reactor. The reef chemistry calculator online will tell you when your levels are balanced, and will even tell you how much of a given product to use to get each level to your target.

[hobogato]

sorry, wasnt trying to imply the see-saw effect, i just meant that if you increase one of them, at some point the other one must decrease or there will likely be a precipitation event.

[Texreefer]

the following is a quote from the link i previously provided

"

Alkalinity (http://www.advancedaquarist.com/issues/feb2002/chemistry.htm) (due to bicarbonate and carbonate but not borate, so those using Seachem salt must raise this value substantially to accommodate the borate being counted in standard alkalinity tests)
2.5 - 4 meq/L or 7 - 11 dKH or 125 - 200 ppm CaCO3 equivalents
Calcium: (http://www.advancedaquarist.com/issues/mar2002/chem.htm)

380 – 450 ppm calcium ion or 950 - 1125 ppm CaCO equivalents
If you are anywhere within these ranges for both parameters, you do not need to perform any correction on your tank chemistry, though you may choose to do so for other reasons. In this sense it makes no difference what the relationship is between the two values. If alkalinity is 4 meq/L, it is not inherently any “better” for calcium to be at 380 ppm or 450 ppm. Also, these ranges are somewhat arbitrary, especially at the high end. In fact, the primary reason for having a high end at all is that it is often difficult to keep one of these parameters above the minimum end of the range if the other is over the top end.So if one of these parameters is slightly above the high end, and the other is OK, that is not a problem worth worrying about.

One of the reasons that you may find compelling to adjust values even when within the recommended range (or outside but close to it) relates to test kit errors. All measurements of calcium and alkalinity have some uncertainty associated with them. Even if the kit is a reliable one, you may still want to strive to be in the center of the range to make it less likely that you are actually outside of it and only appear to be inside of it due to uncertainties in the measurement. This issue is especially important at the low end of the ranges, and not so important at the high ends. "

[matt]

That's a really good pont abut the test kits. Try checking Ca every day for a while, maybe using some different test kits. It will likely seem as if your Ca level is fluctuating around quite a bit, but really it's just inaccuracy in either the kit itself or fluctuation in the testing. All drops are not exactly the same volume.

[Bill S]

And be careful adding stuff. Everytime I do, something ugly seems to happen. As I don't dose Kalk (I don't have a Kalk stirrer...) I add small amounts of anhydrous baking soda (baked for an hour at 300 degrees) which increases alkalinity AND pH. Offsets my Ca reactor, which adds Ca and decreases pH.

[erikharrison]

Matt, I totally got you and completely appreciate such a good explanation. Ace and I know each other and he knows that I am a newb :)
Mike, right on :D

Thanks for leading me towards having a grasp of reef chem. I feel that I am learning at a fairly rapid pace, and I am about ready to buy a CA reactor. I would like to know what other pitfalls that I need to be weary of in the coming months. I am going to buy another pfo mini from another MAASTARD, so I will be squared away there, and the next two major purchases will be a CA reactor and a RK2.

After I am able to sustain a sps colony for a few months, I will look further into purchasing a Bubble King!

[matt]

And be careful adding stuff. Everytime I do, something ugly seems to happen. As I don't dose Kalk (I don't have a Kalk stirrer...) I add small amounts of anhydrous baking soda (baked for an hour at 300 degrees) which increases alkalinity AND pH. Offsets my Ca reactor, which adds Ca and decreases pH.

If you use a Calcium reactor, and add sodium carbonate, what are you adding to also increase Ca? The reactor adds both Ca and alk in a balanced way; if anything, it leans towards raising alk levels more noticably than Ca. Then you're adding more alk through sodium carbonate? You should be adding a balanced addition of Ca and Alk; like using CaCl in addition to the sodium carbonate. Otherwise, your alk might be much higher than you Ca levels.

Two quick points; one, if you use oceanic salt, it's pretty high in Ca and if you do a lot of water changes, maybe you don;t need much Ca to keep your level high enough. Two, if your Ca reactor is adjusted right, it should not lower your tank ph below normal NSW levels. I suspect, if you need to add alk supplement but not Ca, and if your tank ph is low, you might be running a reactor effluent ph that's a little on the high side, which causes you to add more effluent but is not as efficient in raising alk levels because the effluent itself has much lower alk. I found that with my reactors and ARM media, effluent ph of 6.65-6.7 yielded effluent in the 25-30dkh range, which will really keep your tank alk nice and high.

[Bill S]

Matt,

My Ca and Mg are always fine - 400+ for Ca, using the reactor. As someone noted above, I'm generally consuming more Alk than Ca. I do 37 gallon water changes about every week to 10 days, and use Reef Crystals. I don't dose Kalk except occasionally manually - I'm still waiting on my reactor that I'm having built... As my Alk has been a problem AND my pH borders on the low side from the Ca reactor. I've been using ANHYDROUS baking soda, in small quantities, which increases the pH AND the Alkalinity.

[matt]

Bill, have you checked your reactor ph? If it's any higher than 6.7, try increasing the CO2 flow a little and/or slowing down the effluent drip. That might help with the alkalinity.

Anhydrous baking soda (baked baking soda) is sodium carbonate, I believe. When you bake it you drive the CO2 out, which is why it raises your ph. If you're using a reactor, you really should not need to add any. But, if it's working for you, that's the way it goes. Most people deal with calcium reactor ph issues with KW, which only adds carbonate by reacting with CO2 in the water; making it a nice match with a calcium reactor that's supplying plenty of dissolved CO2 in the tank.