Regulating Alk while using a Sulfur Denitrator.

[DipSpit]

Just wanted to share my train of thought and to gather (hopefully) some experience.

The Denitrator consumes alk. This I know - but using it with a 1:1:1:1 part system ( use triton) presents the dilemma of upsetting the balance.

My work around is to have an additional alk dose apart from triton strictly to offset the Denitrator consumption.

Does this sound logical? Am I on the right track? How much alk should I expect to compensate? Any and all info appreciated.

 

[Dennis Cartier]

I just recently took a sulfur reactor offline. I did experience the alkalinity consumption that you are planning for. Unfortunately, it was only after my calcium and magnesium started to rise that I investigated the cause and discovered the extra alk usage from the sulfur reactor. To account for the extra alk, I simply had 2 dosing patterns setup. One using kalk to supply Alk/Ca and one using just the alk part of a 2 part. This setup halted the rise of the Ca and Mg. In your case, I would dose the Triton additives in a 1:1:1:1 and use calcium as the indicator for those additives, and then dose a plain 2 part alk solution to set your alk. I did the equivalent, but used kalk instead of the triton.

I took the sulfur reactor offline due to the mismatched alk consumption. However I am a bit surprised at how good of a job it was doing at keeping my nutrients in check. This became apparent when my No3 rose from 2.5 to 10 and even my PO4 has more than doubled. Is seems the reactor was doing a lot more than I would have ever given it credit for.

 

[DipSpit]

Calcium would be a bad indicator though since the Denitrator adds extra. I'm not worried about higher calcium. I'm pretty sure it wont harm anything

 

[Randy Holmes-Farley Verified Community Expert]

Just wanted to share my train of thought and to gather (hopefully) some experience.

The Denitrator consumes alk. This I know - but using it with a 1:1:1:1 part system ( use triton) presents the dilemma of upsetting the balance.

My work around is to have an additional alk dose apart from triton strictly to offset the Denitrator consumption.

Does this sound logical? Am I on the right track? How much alk should I expect to compensate? Any and all info appreciated.

It’s reasonable, sure, but perhaps unnecessarily complicated.

You can’t know how much you need without measuring alk. It might just be lost in the background noise of the other dosers unless nitrate is very high and coming down fast.

 

[DipSpit]

It’s reasonable, sure, but perhaps unnecessarily complicated.

You can’t know how much you need without measuring alk. It might just be lost in the background noise of the other dosers unless nitrate is very high and coming down fast.

Well not course I measure alk. Should've clarified. Alk was stable via triton. Then a noticed a decrease once the Denitrator was added can assume it was solely due to the addition.

So I now dose that much extra alk to offset the Denitrator addition. Will this work?

Only problem comes in with adjust for actual coral growth. Will the Denitrator only consume a fixed amount of alk?

 

[Randy Holmes-Farley Verified Community Expert]

Well not course I measure alk. Should've clarified. Alk was stable via triton. Then a noticed a decrease once the Denitrator was added can assume it was solely due to the addition.

So I now dose that much extra alk to offset the Denitrator addition. Will this work?

Only problem comes in with adjust for actual coral growth. Will the Denitrator only consume a fixed amount of alk?

The denitrator reduces alk a fixed amount for each ppm of nitrate removed. If that is stable, the alk depletion is stable. If not, then it won't be.

 

[Dennis Cartier]

Randy, ever since I became aware of this extra alk consumption, I wondered about other forms of denitrification. is this limited only to sulfur driven denitrification?

Dennis

 

[Randy Holmes-Farley Verified Community Expert]

Randy, ever since I became aware of this extra alk consumption, I wondered about other forms of denitrification. is this limited only to sulfur driven denitrification?

Dennis

Yes.

Denitrification and nitrate uptake to form organics normally add alk, the exact same amount that got depleted when the nitrate was formed from ammonia, so most of the time, a stable nitrogen cycle doesn't impact alk:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-12/rhf/index.htm

1. 
   (1) NH3 + 2O2 --> NO3- + H+ + H2O

For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

However, the news is not all bad. When this nitrate proceeds further along the nitrogen cycle, depleted alkalinity is returned in exactly the amount lost. For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

1. 
   (2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2
   

In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

1. 
   (3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-
   

Again, one bicarbonate ion is produced for each nitrate ion consumed.

 

[Randy Holmes-Farley Verified Community Expert]

Sulfur denitrator:

Nitrate in the Reef Aquarium - REEFEDITION
http://www.reefedition.com/nitrate-in-the-reef-aquarium/

In these systems, bacteria use elemental sulfur and produce N2 from the sulfur and nitrate according the following equation (or something similar):

2 H2O + 5 S + 6 NO3– → 3 N2 + 5 SO42- + 4 H+

The production of acid (H+) in this reactor can tend to reduce the aquarium alkalinity. It has also been suggested to pass the effluent of such a reactor through a bed of aragonite to use the acid (H+) produced to dissolve the calcium carbonate, and thereby provide calcium and alkalinity to the aquarium. While that is a fine idea, it doesn’t add much calcium and alkalinity to most aquaria.

To estimate the magnitude of the effect, we start with a liberal estimate of how much nitrate might be removed. Say 10 ppm of nitrate per week.

10 ppm nitrate = 0.16 mmole/L of nitrate

Since 4 moles of H+ are produced for every 6 moles of nitrate consumed, this will produce

0.107 mmoles/L of H+ per week

How much calcium this could produce?

Assume that it takes one proton to dissolve one calcium carbonate:

CaCO3 + H+ → Ca2+ + HCO3–

Clearly, this is a substantial overestimate because much of the acid will be used up driving the pH down to the point where CaCO3 can even begin to dissolve. Consequently, we have an upside limit of 0.107 mmoles of Ca2+ per week. Since calcium weighs 40 mg/mmol, that’s 4.3 ppm Ca2+ per week.

 

[DipSpit]

The denitrator reduces alk a fixed amount for each ppm of nitrate removed. If that is stable, the alk depletion is stable. If not, then it won't be.

Depends oh... Flow rate?

 

[Randy Holmes-Farley Verified Community Expert]

Depends oh... Flow rate?

Depends on nitrate level too.