Seachem Reef Salt and Alkalinity

I use Seachem Reef Salt for my tank, which I understand has fairly high borate concentrations. Thanks to a great recommendation by Corailline, I now have a Hanna alkalinity checker. My understanding of the Hanna unit is that it reports total alkalinity, which could result from a number of anions, including bicarbonate and borate.

If I'm not mistaken, the typical assumption is that most of the alkalinity for a saltwater tank is from bicarbonate, and therefore one can inter-convert between ppm CaCO3 and carbonate hardness.

My thinking is that, since Seachem's salt is unique in its high borate levels, the alkalinity reported by my Hanna checker will include both carbonate hardness and borate hardness.

For example, I'm getting a reading now of 212 ppm from the Hanna unit. If we could assume all of this alkalinity was due to bicarbonate, then I could readily convert this number to dKH = 11.8. I understand from Seachem's website, however, that borate accounts for as much as 40% of this number, meaning the actual carbonate hardness is more like 7.2.

Is my thinking correct? And if so, is the number I'm really trying to target the total alkalinity or the carbonate hardness?

 

Bump for those who might also use this salt or understand the chemistry better than I do . . .

 

The first time I read the post yesterday it made my brain hurt. Now I am scared to read it again.

Basically you're looking at the total value your dkh is correctly 11.8.

I am a dyslexic, left handed, failure at math, chem I do ok at so I will give another go, but I am confident that your total "the alkalinity reported by my Hanna checker will include both carbonate hardness and borate hardness" is correct.

You have the Randy Holmes Farley link right?

http://reefkeeping.com/issues/2004-05/rhf/

Don't make me post the Randy Holmes Farley ORP link Juston!!!!!

 

RHF is probably the best person to even answer this one. I use the seachem reef salt and I really like it . it is affordable and I feel I am getting pretty good results from it. that said, I do have to supplement to keep my alk in the 8.5 range 175 range on my hannah.

I guess my question is does the Hannah read the calcium carbonate levels in the water or does it also read the alkalinity that the borate offers.

 

I will see if I can get RHF to wander over this way.

 

Yeah, absolutely. So I'm correct in my thinking. The question is this, fundamentally, for Seachem salt - for a given alkalinity, Seachem will have a lot more borate relative to carbonate/bicarbonate than other salts. Which means if I shoot for, say, an alkalinity of 12, the total contribution of carbonate/bicarbonate to the alkalinity might be 60% or so. In my mind, that means there is less carbonate available for coral growth.

In fact, Randy Holmes alludes to this in his post about alkalinity and specifically references Seachem's salt. The real question is - are we ultimately targeting a specific concentration of all buffers (carbonate, bicarbonate, borate, silicate, etc) to achieve a certain buffering capacity or is what we are really after the concentration of carbonate/bicarbonate, specifically - which functions both as a buffer AND an essential building block for coral growth. If carbonate/bicarbonate is the goal then when we say, "target an alkalinity of 8," with the inherent assumption that 95%+ of that alkalinity comes from carbonate/bicarbonate, then Seachem's salt will be relatively low in carbonate/bicarbonate.

Hope that makes sense? In short, total alkalinity from the Hanna meter (and any other test that measures total alkalinity) will include a number of compounds. For most salt, the alkalinity measurement will reflect mostly the carbonate/bicarbonate concentration. For Seachem, I think as much as 40% of the reported alkalinity comes from borate. I'm not sure what advantage Seachem feels is offered by such high borate concentrations, but I think it throws the rule of thumb alkalinity values out the window if the real goal is to determine the concentration of carbonate and bicarbonate.

 

I got a response back from Hanna and they confirmed that their unit reads TOTAL alkalinity (the sum of contributions from any anion that contributes to alkalinity, including borate, carbonate, bicarbonate, silicate, etc). So the previous question still stands. Are we REALLY trying to adjust the alkalinity or just hit a target carbonate/bicarbonate concentration (for which alkalinity is usually a reasonable surrogate, but not in the case of Seachem salt).

 

Aaaahhhhhh

 

I used Seachem Reef Salt once and I had issues with keeping the alkalinity stable. Each time I would first mix the salt up in the bucket before measuring it out and adding to the rodi. I mixed a batch to 1.026 and it had alk of 10, the next batch had 7.2, then the next batch had 15 something. I stopped using the salt because I couldn't get it to mix the same each time.

Maybe the borate levels is what skewed it all along, but either way it was too stressful for me and my coral.

 

This great article answers my question. In brief, we aren't so concerned about alkalinity. We are concerned about the concentration of carbonate and bicarbonate. For Seachem salt, because they have so much borate, the alkalinity test does NOT tell you what you need to know about carbonate/bicarbonate. This might explain why Seachem recommends the aquarist target an alkalinity of 4-5 meq/L. In carbonate hardness terms, that would equate to a dKH of 11.2 to 14. This higher-than- normal recommendation probably accounts for the presence of borate.

http://www.advancedaquarist.com/2002/2/chemistry

To quote Randy Holmes-Farley from his article:

"So what we are doing is using a very simple alkalinity test as a surrogate measure for bicarbonate and carbonate. Since these two substances comprise the great majority of alkalinity in seawater, it is safe for most people to equate alkalinity with "availability of bicarbonate and carbonate for my corals".

There are, however, some important caveats to that equation. Some of these were described above, such as salt mixes that have excessive borate. Such complications make it difficult to know how much of the measured alkalinity is bicarbonate and carbonate, and thus it is difficult to know if you are satisfying the needs of the corals [Hence the unusually high alkalinity recommendations by Seachem]."