sulfur denitrator and Alk

BLockamon

New member
Randy,

Have you seen any data on the impact of a sulfur denitrator on Alkalinity? I dose kalk to maintain calcium/alk, and they are usually right in line. However, after using my denitrator for a little over a month, calcium is up to ~490 and alk is down to ~6 DKH.

On a separate forum, someone else posed a warning that his sulfur denitrator dropped the alk.

Is this just anectodal coincidence or is there some impact from the denitrator? Maybe the high calcium content of the reactor (it is buffered with aragonite) is causing some precipitation. I'm kind of skeptical since I don't notice a low of residue and the pH is still pretty low (~7-7.5).

In any case, do you think dosing the Alk part of a 2-part to maintain Alk balanced with Ca would be OK in the long run? If not, I may have to look at another option to balance out the chemistry.
 

Randy Holmes-Farley

Reef Chemist
Premium Member
Sulfur denitrators will reduce alkalinity. It is a fundamental part of the process. If you buffer it perfectly (not sure that can happen) with aragonite that just shifts it to a calcium rise rather than an alkalinity loss. I discuss it here:

Nitrate in the Reef Aquarium
http://www.advancedaquarist.com/issues/august2003/chem.htm

A two part is probably the best way with a sulfur denitrator, since you can just stop the calcium part for a little while if calcium ever rises too much as a consequence of making up for alkalinity loses with the two part.
 

boxfishpooalot

New member
n a separate forum, someone else posed a warning that his sulfur denitrator dropped the alk.

That would be me :D fwiw, I just use baking soda strait into the sump, or via top off water to increase the alkalinity. My calcium has remained at 500ppm for over a year. :)
 

BLockamon

New member
boxfishpooalot, I presume that as the nitrate levels in the tank drop, the impact on the alkalinity should drop as well, since less sulfuric acid will be released. Can you confirm?
 

boxfishpooalot

New member
Yes as the nitrates decline and their food source diminishes, the alkalinitly would be consumed less. At least thats what I expect.

From Randys article:

2 H2O + 5 S + 6 NO3- 3 N2 + 5 SO4-- + 4 H+

Here is my rudamentary look at it:

2 H2O- they use water
5 S - use molecules of sulfur
6 NO3- - Convert No3 to:
3 N2- nitrite,
SO4-- - Sulpheric acid
4 H+ - Acid-or your drop in alk

As you see im no chemist :lol: Maybee Randy can help out here. But im sure once the nitrate is gone the will be a reduction in alkalintiy usuage.
 

Randy Holmes-Farley

Reef Chemist
Premium Member
Nitrate levels may drop to low steady state levels, but that does not mean that the denitrator is not continually taking out more nitrate and converting it just as fast as it is being produced in the tank. So the effect on alkalinity will be ongoing, and dependent on how much nitrate is being taken in by the denitrator, although I agree that there will likely be a burst at the start as initially high nitrate levels are dropped.
 
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