why do we measure both Ca++ and alkalinity

[yraveh]

Good morning.
Randy, in his article http://reefkeeping.com/issues/2002-04/rhf/feature/index.php), states that the normal precipitation ratio of Ca++ to alkalinity is 20 ppm: 1 meq/L respectively. using this ratio, Randy defines "balanced" salt water and supplemnets.
I am wondering for a while about the title. if we start from a "balanced" salt water and use "balanced" supplement such as lime or 2 parts, then it should be enough to monitor ca++ or alkalinity, but not both. since they go up or down in a balanced manner.

 

[Scorpius]

In a perfect world yes, but every tank is different. I've had calcium get consumed more at times and then consumption drops off. Same thing for alkalinity.

I run 8.4dkh 430 Ca.

Here's a handy ratio for balance

DKH Ca
4.50 393
4.75 395
5.00 397
5.25 398
5.50 400
5.75 402
6.00 404
6.25 405
6.50 407
6.75 409
7.00 411
7.25 413
7.50 414
8.00 418
8.25 420
8.50 422
8.75 423
9.00 425
9.25 427
9.50 429
9.75 431
10.00 432
10.20 434
10.50 436
10.75 438
11.00 439

 

[Ron Reefman]

Nice chart, thanks.

 

[Scorpius]

Nice chart, thanks.

No problem, I saved it myself when another fellow reefer posted it. :thumbsup:

 

[bertoni]

The ratio of consumption can be off a bit, as stated:

http://reefkeeping.com/issues/2004-12/rhf/index.htm

Also, our supplement can be a bit off, and water changes skew the ratio, too. I only measured calcium and magnesium every couple of months or so, and it never varied much, at that, though.

 

[RobZilla04]

Ditto, thx for the chart. Helps when the color is tough to see on one of the tests. Now I can ballpark if I'm balanced or not.

 

[zsuman101]

i test everything once a month, calcium once a week, alkalinity twice a day ... my reef eats alkalinity

 

[yraveh]

The ratio of consumption can be off a bit, as stated:

http://reefkeeping.com/issues/2004-12/rhf/index.htm
.

i was not aware of this article.
thanks for the link.

 

[bertoni]

You're welcome!

 

[jason2459]

I would advise against chasing those numbers in that chart posted above. There is no required ratio just a general range to be in. Randy has agreed as well with that statement more then once in recent conversations.

Reef Aquarium Water Parameters
http://reefkeeping.com/issues/2004-05/rhf/

 

[Timfish]

+1. Alkalinity and calcium may change in tandem or may change in opposite directions. Alkalinity is used for photosynthesis so is used by all photosynthetic algae. Alkalinity may also be the primary source for calcium for calcification for some corals so even in a perfect world that ratio of 20 mg/l of calcium to 1 meq/l of alkalinity may not be correct. The DOC produced by algae and corals is converted by cryptic sponges into alkalinity. Bottom line is there's a lot of stuff going on in our tanks besides just growing corals. We need to stay on top of alkalinity, calcium and magnesium and pH but it's more important IMO to look at our animals and systems and track how they are performing over time. Not worry what day to day or week to week numbers are.

 

[tmz]

There is no optimal precise practical ratio for alk and calcium . Keeping alk constant at a point of your choice within the recommended range of 7to 11 dkh is key.NSW is around 7dkh. Calcium is needed and can be as low as 380ppm or as high as 500ppm without issues. (recommended range is 380 to 450ppm)

 

[tmz]

Alkalinity may also be the primary source for calcium for calcification for some corals so even in a perfect world that ratio of 20 mg/l of calcium to 1 meq/l of alkalinity may not be correct.

????

Not sure what you mean; there is no calcium in alkalinity.

 

[tmz]

Alkalinity is used for photosynthesis so is used by all photosynthetic algae

???

The chemical equation for photosynthesis is :

6 CO2 + 6 H2O → C6H12O6 + 6 O2

Where:
CO2 = carbon dioxide
H2O = water
light is required
C6H12O6 = glucose
O2 = oxygen

http://chemistry.about.com/od/photo...nced-Chemical-Equation-for-Photosynthesis.htm

No indication of alk uptake there.

 

[bertoni]

The ratio of 20 ppm Ca⁺⁺ per 2.8 dKH is based on the ratio in calcium carbonate. Some of the calcium will be replaced by magnesium and strontium, and that'll shift the ratio a bit, usually very slightly.

As stated, photosynthesis does not consume alkalinity. The uptake of nitrate consumed alkalinity temporarily, but the metabolic process releases it fairly quickly.

The article I linked goes into details.

 

[Timfish]

Alkalinity may also be the primary source for calcium for calcification for some corals so even in a perfect world that ratio of 20 mg/l of calcium to 1 meq/l of alkalinity may not be correct.

????

Not sure what you mean; there is no calcium in alkalinity.

I really hate eating crow, especially when it was so stupidly wrong. :uhoh2:
My only defense is found this paper about 2 or 3 AM when I couldn't sleep and just skimmed through the abstract and never went back to read it.

http://dl.uncw.edu/etd/2008-3/r1/juryc/christopherjury.pdf

 

[Timfish]

Alkalinity is used for photosynthesis so is used by all photosynthetic algae

???

The chemical equation for photosynthesis is :

6 CO2 + 6 H2O → C6H12O6 + 6 O2

Where:
CO2 = carbon dioxide
H2O = water
light is required
C6H12O6 = glucose
O2 = oxygen

http://chemistry.about.com/od/photo...nced-Chemical-Equation-for-Photosynthesis.htm

No indication of alk uptake there.

HCO3- (alkalinity, DIC) is the primary source for CO2 at the pH we typically see on reef systems.

For starters scroll down to the section on direct uptake of bicarbonate (about halfway down):
http://reefkeeping.com/issues/2006-10/rhf/index.php

Carbonic anyhdrase which is used for stripping off the CO2 molecule is found in all marine algae:
https://www.ncbi.nlm.nih.gov/pubmed/4977463

And an experiment on alkalinity increasing photosynthesis in corals:
https://www.ncbi.nlm.nih.gov/pubmed/27041045

 

[bertoni]

It's true that corals will take up bicarbonate for carbon dioxide, but they release the alkalinity back into the water column fairly quickly, as they require only the carbon. The net effect on alkalinity is zero.

 

[Jone]

tag

 

[tmz]

It's true that corals will take up bicarbonate for carbon dioxide, but they release the alkalinity back into the water column fairly quickly, as they require only the carbon. The net effect on alkalinity is zero.

I agree alkalinity is not used by photosynthetic activity though it's form may change from bicarbonate to hyrdoxide or a reduction in H+ momentarily with zero effect on alkainity and ultimately no change in the carbonate /bicarbonate/acid contiuuum as less H+ or more hydroxide will shift it back toward carbonate /bicarboante.

As much is stated in the referenced article by Randy in the bicarb uptake section:


"....The hydroxide is then pumped out, or H+ is pumped in, to achieve pH balance...."