calcium high, but I don't dose calcium

[renab]

Alk

Alk

first off there is no such thing as pH buffer in saltwater they are all alkalinity buffers dont chase pH. Also reef builder contains cal and mag along with few other elements. this is the cause of high cal.

First, alkalinity is a measurement of buffering systems (there are multiple) in (in this case) marine systems. Was the buffers don't chase pH supposed to be buffers don't change pH? That's the point of a buffer. To absorb protons ie (H+) so the pH doesn't change, however if you exhaust the alkalinity, your pH will go down. As, you exhaust it, it can be seen to slowly increase the pH. They are tied together.

So, you place HCO3- in your tank. This is a buffer it absorbs protons, to become H2CO3 (mostly non-dissotiated, in the tank), but that has a pKa value that will release some protons, if the concentration becomes too high. ie you run through the number of them available in the tank. Phosphates are also a buffering system (although we don't like them), and phophoric acid doesn't make a great buffer anyway, because the first proton that dissociates is fairly strong.

Anyway, the point is that if your alk goes down (ie your buffering system gets exhausted) your pH will go up.

I do agree with the CO2 being high causing pH shift, but that is this reaction:

CO2 + H2O makes H+ and HCO3- (one step of many in the above buffering system--measured by alk)

 

[Bacon_Boss]

May I ask what test kit youre using?

 

[bertoni]

Anyway, the point is that if your alk goes down (ie your buffering system gets exhausted) your pH will go up.

I think you meant the pH will go down. The buffering in our tanks raises the pH.

 

[Dr. Reef]

I have seen many tanks with alk levels as low as 4-5 dkh holding pH of 7.8 and up.

 

[tmz]

Chasing pH with carbobnate buffers is a poor method it raises alk and has only a short temporary effect on pH unless the alk is quite low at the start. The changes in alk can do more harm than pH at the low end of an acceptable range ,say 7.8 or higher. CO2 drives the pH not the alkalinity.

If you try to manage pH with carbonate buffers the effect on pH is transient and short lived as CO2 from the air equilibrates in a matter of an hour or two and hydrolizes, shifting the carbonate: bicarbonate ratio towards bicarbonate and adding H , leaving higher alkalinity from the carbonate buffer addition and the same low pH.
CO2 does not deplete the additional alkalinity; just the pH : CO2 +H20 ----> CHO3 +H and H + CO3 ---> CHO3. Two new CH03 (bicarbonate ions are added) each with one unit of alkalinity and 1 CO3 ion with 2 units of alkalinity is lost. Net result on alk is zero.Net result on pH is plus two H protons.

 

[Randy Holmes-Farley]

So, you place HCO3- in your tank. This is a buffer it absorbs protons, to become H2CO3 (mostly non-dissotiated, in the tank)

FWIW, the pKa of H2CO3 in seawater is about 5.8 (second pKa about 8.9), so at the pH attained in reef tanks, it is by far in the dissociated states. It is mostly HCO3-, some CO3--, and only a tiny bit of H2CO3 in the range of pH between 7.8 and 8.6 that exist in most reef tanks.

 

[mhsmith]

The testing kits that I am using is my ph probe that is tied to my GHL Proiflux computer. I have calibrated the probe and it may be off by .02 at most. The other testing I am doing is with Hannah instrument alkalinity checker and calcium checker. I use Salifert for testing the magnesium.

 

[Randy Holmes-Farley]

FWIW, a lot of folks have found the Hanna calcium checker unreliable. I've not used it or evaluated it myself.

 

[mhsmith]

what calcium test kits do you recommend?

 

[bertoni]

I had good results with the IO and Salifert kits, although the Salifert was faster to run.

 

[tmz]

I use and like the Saliofert test.

 

[mhsmith]

So I tested my calcium and alkalinity on freshly made salt water with Seachem Reef salt. Calcium was 499 ppm and Alkalinity was 111ppm. This was using the Hannah checker test kit.

 

[Randy Holmes-Farley]

What was the salinity? The alk seems a tad low for 35 ppt seawater, but it is likely fine to use.

 

[Bacon_Boss]

I'm a fan of the Saliofert personally, I was praying you werent going to say API, had one tell me that my calcium was 600<. Used my buddies Saliofert and it read 330.

 

[tmz]

Sorry I misspelled it ;it's Salifert.

 

[tmz]

499ppm calcium and only 6.2 dkh(111ppm) alk seem off for 35ppt?1.026 sg.

 

[mhsmith]

The salinity was 1.025. I will check the alkalinity again when I get home and make sure.

 

[Randy Holmes-Farley]

Seems like the alkalinity is either off in the salt mix, or the testing was off.

 

[mhsmith]

Just checked again. This time I got 116ppm with salinity 1.025

 

[mhsmith]

Did it again with Instant Ocean test kit and got 2 meq/l close to the same reading as above.