Why does Ph fluctuate during the nitrogen cycle?

[Cooper5054]

Hello!

First post on R2R.

I have seen many answers on various forums and articles that say a reefer should not be worried about Ph during the nitrogen cycle. I would like to know why so that I can better understand ph and water chemistry.

Why does ph change during the cycle? If ph is just a measure of hydrogen ions in the water, what causes more hydrogen during the cycle? Is hydrogen a biproduct of the nitrogen cycle? Can the increased bacteria that is blooming be starving oxygen out of the water? If there is nothing in the water to turn bicarbonate into carbonate, then it surely cant be a result of lowering alk.

Any knowledge, articles, or insight would be appreciated.

 

[blaxsun]

Because you shouldn't be worried about pH during cycling.

 

[flyingscampi]

This might help? I think it says nitrification lowers the pH but can easily be countered by gas exchange?

The Influence of pH on the Nitrification Rate - Nitrogen Removal

In the literature, the optimum pH value forthe nitrification process varies between 8 and 9. Figure 3.7 summarizes investigations of pH effects on the

www.climate-policy-watcher.org

 

[gbroadbridge]

Hello!

First post on R2R.

I have seen many answers on various forums and articles that say a reefer should not be worried about Ph during the nitrogen cycle. I would like to know why so that I can better understand ph and water chemistry.

Why does ph change during the cycle? If ph is just a measure of hydrogen ions in the water, what causes more hydrogen during the cycle? Is hydrogen a biproduct of the nitrogen cycle? Can the increased bacteria that is blooming be starving oxygen out of the water? If there is nothing in the water to turn bicarbonate into carbonate, then it surely cant be a result of lowering alk.

Any knowledge, articles, or insight would be appreciated.

I believe some reasons are mentioned in this article.

http://www.reefkeeping.com/issues/2004-09/rhf/

 

[Randy Holmes-Farley Verified Community Expert]

Welcome to REEF2REEF!

The cycling of ammonia to nitrate produces acid that lowers pH and alkalinity. This article has more details.

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

Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

1. (1) NH3 + 2O2 à 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 à 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 CO2into macroalgae to form typical organic molecules:

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

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

It turns out that as long as the nitrate concentration is stable, regardless of its actual value, there is no ongoing net depletion of alkalinity. Of course, alkalinity was depleted to reach that value, but once it stabilizes, there is no continuing alkalinity depletion because the export processes described above are exactly balancing the depletion from nitrification (the conversion of ammonia to nitrate).

There are, however, circumstances where the alkalinity is lost in the conversion of ammonia to nitrate, and is never returned. The most likely scenario to be important in reef aquaria is when nitrate is removed through water changes. In that case, each water change takes out some nitrate, and if the system produces nitrate to get back to some stable level, the alkalinity again becomes depleted.

 

[birdsnest]

Why does ph change during the cycle? An increase of hydrogen ions in the water. If ph is just a measure of hydrogen ions in the water, what causes more hydrogen during the cycle? Ammonia oxidation by ammonia oxidizing bacteria. Is hydrogen a biproduct of the nitrogen cycle? Yes. Can the increased bacteria that is blooming be starving oxygen out of the water? Yes. Aeration is very important. And there are other limiting factors in the nitrification cycle. The quote below came from an old email that shed light on tank cycling.

Outside of phosphate deficiencies there are three "usual suspects" in the way of limiting factors of nitrification assuming all of the appropriate bacteria are present and have colonized a substrate: carbonates, bicarbonates, and oxygen, so even if your alkalinity is high from bicarbonate additions I suspect that if you have been using bicarb alone you may be lacking in carbonates...I usually like to make a good ol' 1:6 soda ash/bicarb buffer mix, or a 1:4:24 mix of sodium tetraborate (borax)/soda ash/bicarb ...might be worth a shot to see if carbonates are the missing component that is causing your cycling to lag.



Also oxygen can be limiting, but this is less common. Especially during cycling I like to over-oxygenate to help speed things along (to the point where I have rolled up a Dewar flask of LOX for big systems and pumped tons of O2 in through a ceramic micro-diffuser). It's also important to note that when examining if your O2 levels might be suboptimal you can easily be confused by taking a single reading, for example if you grab a DO measurement in the morning and you're sitting at 95% saturation you may think everything is optimal...but often DO will fluctuate significantly over the course of a day, the simple act of feeding (depending on the stocking and feed rates) can cause DO to slowly taper off down to the low 70's before ramping back up...this can be especially prevalent in smaller systems where any surface oils and lipids play a bigger role in gas exchange and inhibition can be magnified.



...for example a 1000L system that has a 6-8 hour depression in DO post-feeding will have over 1000mg less available oxygen for nitrification over the course of a day, which can cause our hypothetical 1000L tank that is just barely keeping up with the bioload to go from 0 mg/l NH3 to 0.5 mg/l NH3 in just 24 hours ...when in doubt more O2 always helps!

 

[Cooper5054]

Welcome to REEF2REEF!

The cycling of ammonia to nitrate produces acid that lowers pH and alkalinity. This article has more details.

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

Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

1. (1) NH3 + 2O2 à 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 à 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 CO2into macroalgae to form typical organic molecules:

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

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

It turns out that as long as the nitrate concentration is stable, regardless of its actual value, there is no ongoing net depletion of alkalinity. Of course, alkalinity was depleted to reach that value, but once it stabilizes, there is no continuing alkalinity depletion because the export processes described above are exactly balancing the depletion from nitrification (the conversion of ammonia to nitrate).

There are, however, circumstances where the alkalinity is lost in the conversion of ammonia to nitrate, and is never returned. The most likely scenario to be important in reef aquaria is when nitrate is removed through water changes. In that case, each water change takes out some nitrate, and if the system produces nitrate to get back to some stable level, the alkalinity again becomes depleted.

I asked this question in another sub and was directed here. Do I have your permission to post this response elsewhere?

 

[Randy Holmes-Farley Verified Community Expert]

I asked this question in another sub and was directed here. Do I have your permission to post this response elsewhere?

At REEF2REEF you can repost it anywhere. At other sites, just post the link.