Alkalinity stability? pH stability? Are they even different?

[arking_mark]

That is an interesting method! But in our case we prefer not to lower the ph at all only to raise it. I don't think there is any scenario where we are actually wanting to suppress the pH because it is too high.

We let the ph get as high as it can during the day time and then attempt to maintain that ph Stability over the night time hours so that every day and night it is always the same (high). I could see your method being useful if we had the opposite scenario (we were wanting to lower it because it was rising uncontrollably or something to that effect).

Could also see it being helpful to 'stabilize' (not necessarily stabilize-high) the at-home pH levels of a smaller reef aquarium with less consumption (not possible to dose enough additives to keep it stable-high).

I guess I should have clarified though that we want to stabilize it at a high level, rather then just stabilize it period.

I've looked to keep my pH stable. I used to elevate beyond 8.3, but found too much abiotic precipitation. 8.2 seems to be a sweet spot for me, as I'm not trying to accelerate growth.

 

[Lasse]

In terms of alk and nitrate, it takes a 50 ppm drop in nitrate to add 2.3 dKH.

Is this because of denitrification?

I use Triton Core 7 as balling method. Core 7 use sodium carbonate as alkanity component. This will rise pH without limits. Because of that - I test to only dose during night time in order to stabilize the pH around 8.2 - it works well but instead I got an alkalinity variation of nearly 2 dKH on a 24 hours period. I changed back to try to dose in order to keep a steady KH instead

Sincerely Lasse

 

[ReefChasers]

Is this because of denitrification?

I use Triton Core 7 as balling method. Core 7 use sodium carbonate as alkanity component. This will rise pH without limits. Because of that - I test to only dose during night time in order to stabilize the pH around 8.2 - it works well but instead I got an alkalinity variation of nearly 2 dKH on a 24 hours period. I changed back to try to dose in order to keep a steady KH instead

Sincerely Lasse

You are probably running into the issue i detailed about consumption. You need a massive amount of alk/calcium demand from stony corals in order to totally offset the night time fall with chemical dosing. The higher you keep things running of course also seems to be more and more demand for dosing which i guess is to be expected and probably a "good thing" but it also seems like riding the edge of "out of control" which can be a dangerous place to be.

It does seem as if alkalinity AND ph are very difficult to stabilize together. It does seem easier to achieve 8.2 stable with stable dkh then it does to achieve 8.4 stable with stable dkh because of a couple of factors.

The question of which one is better to stabilize is an interesting one I am aware of at least one scientific paper (dont have link handy) that suggests it didnt seem to matter much which one was stable but that it seemed good to stabilize them. I do not believe article explored "stabilizing both" as we are discussing here.

Also with only night time dosing you do have this situation that seems like the dKh rise at night and fall during day but i dont think those 0.5 pts shift matter all that much, all else being stable.

If tank has a lot of consumption requirements than stabilizing dkH and pH seems very possible, but parking pH at 8.2 seems safer/easier than pushing for 8.4. Corals can certainly thrive with stable 8.2 ph it is hard goal for many to achieve. Stable 8.4 is a pipe dream.

You may say I am a dreamer, but I dont think I am the only one! Lol

 

[ReefChasers]

I've looked to keep my pH stable. I used to elevate beyond 8.3, but found too much abiotic precipitation. 8.2 seems to be a sweet spot for me, as I'm not trying to accelerate growth.

I do think 8.2 is a pretty sweet spot pushing higher presents its own problems.

 

[Randy Holmes-Farley Verified Community Expert]

Is this because of denitrification?

I use Triton Core 7 as balling method. Core 7 use sodium carbonate as alkanity component. This will rise pH without limits. Because of that - I test to only dose during night time in order to stabilize the pH around 8.2 - it works well but instead I got an alkalinity variation of nearly 2 dKH on a 24 hours period. I changed back to try to dose in order to keep a steady KH instead

Sincerely Lasse

Any consumption of nitrate (to N2, to ammonia, or to organic tissue) adds that alkalinity.

 

[Lasse]

I did only dose the alkalinity part during night time - the calcium and magnesium was/are spread out during 24 hours. I dose the alkalinity part between 23:00 and 13:00 This is my chart for a week in march when I measured pH, dose and KH (KH - Hanna marine alkalinity checker - here expressed as KH

Today - I dose most of the alkalinity part during daytime and keep the KH stable instead - here a week in march - this year and KH is measured by KH director

In march last year - I was able to calculate the total calcification between 13:00 and 23:00 an it was around 10.7 gram CaCO3 a day

When I start to dose the way I do now - I run some test rounds to see where the most calcification rate happens - my test show that more than 80 % happens between 12:00 and 00:00

Which run has been best - I do not know but there is a gut feeling that it was more growth when I dosed during nighttime but since march last year - I have moved a large clam from the system (around 3 kg)

I run my skimmer with outside air.

Sincerely Lasse

 

[ReefChasers]

I did only dose the alkalinity part during night time - the calcium and magnesium was/are spread out during 24 hours. I dose the alkalinity part between 23:00 and 13:00 This is my chart for a week in march when I measured pH, dose and KH (KH - Hanna marine alkalinity checker - here expressed as KH

Today - I dose most of the alkalinity part during daytime and keep the KH stable instead - here a week in march - this year and KH is measured by KH director

In march last year - I was able to calculate the total calcification between 13:00 and 23:00 an it was around 10.7 gram CaCO3 a day

When I start to dose the way I do now - I run some test rounds to see where the most calcification rate happens - my test show that more than 80 % happens between 12:00 and 00:00

Which run has been best - I do not know but there is a gut feeling that it was more growth when I dosed during nighttime but since march last year - I have moved a large clam from the system (around 3 kg)

I run my skimmer with outside air.

Sincerely Lasse

I feel like if we can achieve stabilized (high) ph and stabilized alk that is definitely the golden goose, corals are going to thrive -- i do feel it is doable with night time dosing but, what Randy is saying about Nitrate comsumption raising the Alkalinity is just about the only thing that makes sense for my situation but also at the same time makes no sense at all.

It seems scientifically impossible that my alk has been rising so much while calcium falling so much. I guess thats why I was giving credence to what that guy on the podcast was saying abour bound up alkalinity due to excess co2 but i absolutely have confidence in Randy's opinion that it is total bullocks.

For me, nitrates have remained pretty stable. In no way can I make sense of how they would explain a 1.5 dkh rise in Alk with a seemingly never ending loss of Calcium (dosing 600ml calcium chloride daily just to maintain -- not dosing any soda ash at all)

Am I correct in my understanding that nitrate consumption caused by organic growth raises dkh but is equally/perfectly offset by dosing (or feeding) those nitrates back?

As far as when corals actually lay down there carbonate skeletons I am not sure is of the most importance -- the point of dosing at night is to simply offset the diurnal ph cycle. I think this will always lead to a slightly elevated alk reading in the AM (since you just got done dosing all night) and a slightly lower Alk reading in the PM (since you havent been dosing all day). That matches my personal observations while doing this method.

Its just confounding to be dosing 600ml of calcium chloride day after day but to have alkalinity on the rise with no additional supplement (besides Kalkwasser) and its got me scratching my head.

For now I am backing off 8.4 dream and being satisfied with a great, stable 8.2

Im sure ill get the itch to take another run at it after these waves stop rockin' the ship. Lol

 

[ReefChasers]

The other thing I may need to consider is that higher alk increases consumption and if I choose a higher dkh stability point then 8.5/9 then the 8.4 stable ph might be easier to achieve. Lets say at a stable dkh of 11 and a stable ph of 8.4.

The only problem with it is it feels a little bit like "riding the lightning" and im not sure if I am ready to be a Thunder God.

 

[arking_mark]

The other thing I may need to consider is that higher alk increases consumption and if I choose a higher dkh stability point then 8.5/9 then the 8.4 stable ph might be easier to achieve. Lets say at a stable dkh of 11 and a stable ph of 8.4.

The only problem with it is it feels a little bit like "riding the lightning" and im not sure if I am ready to be a Thunder God.

Assuming perfect aeration with outdoor air (400ppm CO2), a tank with 7dKH will have a pH around 8.22 NBS. If you increase the alk to 11dKH, that same tank would have a pH around 8.38 NBS.

 

[Randy Holmes-Farley Verified Community Expert]

Some clarification of the nitrate alk connection:

1. production of nitrate from foods or ammonia or N2 depletes alk.

2. Conversion of nitrate back to N2, organic tissue or ammonia adds back alkalinity to the exact same extent it was depleted in #1.

3. Dosing nitrate that is consumed adds alk.

Thus, anyone dosing nitrate will see an alk rise (or a reduction in apparent alk demand relative to calcium).

 

[ReefChasers]

Some clarification of the nitrate alk connection:

1. production of nitrate from foods or ammonia or N2 depletes alk.

2. Conversion of nitrate back to N2, organic tissue or ammonia adds back alkalinity to the exact same extent it was depleted in #1.

3. Dosing nitrate that is consumed adds alk.

Thus, anyone dosing nitrate will see an alk rise (or a reduction in apparent alk demand relative to calcium).

Thanks for that clarification on this. It seems that dosing nitrate is not a great option overall when attempting to stabilize a high pH. Natural feeding process seems like a much better solution overall.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks for that clarification on this. It seems that dosing nitrate is not a great option overall when attempting to stabilize a high pH. Natural feeding process seems like a much better solution overall.

If you need both N and P, yes. One can also dose ammonium hydroxide instead of nitrate, or calcium mixed with the nitrate,

 

[Lasse]

1. production of nitrate from foods or ammonia or N2 depletes alk.

2. Conversion of nitrate back to N2, organic tissue or ammonia adds back alkalinity to the exact same extent it was depleted in #1.

I have seen this statement from you before but I have also seen statement that says that it is only around 50 % that will be returned from denitrification. It is also my experiences after running indoors fish farms with both nitrification and denitrification that there is a steady loss of alkalinity in the system. Here - page 13 in the PDF document, Here - in the introduction and here at chapter 5 - page 3-4

Sincerely Lasse

 

[HuduVudu]

Thus, anyone dosing nitrate will see an alk rise (or a reduction in apparent alk demand relative to calcium).

Can confirm IRL.

 

[Randy Holmes-Farley Verified Community Expert]

I have seen this statement from you before but I have also seen statement that says that it is only around 50 % that will be returned from denitrification. It is also my experiences after running indoors fish farms with both nitrification and denitrification that there is a steady loss of alkalinity in the system. Here - page 13 in the PDF document, Here - in the introduction and here at chapter 5 - page 3-4

Sincerely Lasse

Only the middle link works for me. The others say I've hit the download limit despite never having been to that site before. The middle link clearly lacks good chemical understanding of alkalinity and I would not believe it's conclusions (see next post).

I don't think there are deviations from the 2.3 dKH per 50 ppm nitrate consumed if it is converted into ammonia, most organic N of biological origin (e.g., amines), or N2. It provides one molar unit of alkalinity for each mole of nitrate consumed.

That said, if one converts nitrate into ammonia or amines, that ammonia can become protonated or not, depending on pH. So depending the what ultimately happens to the ammonia, and what the pH is, one might or might not measure a specific change in alk.

If the nitrate is converted into other forms of N, one may or may not expect a change in alkalinity. Forming nitrite from nitrate, for example, has no impact on alk.

 

[Randy Holmes-Farley Verified Community Expert]

Here's what the middle link hypothesizes about alkalinity, which is clearly incorrect and gives me zero confidence in that paper (the first hypothesis is also flawed for exactly the same reason as below):

"Another hypothesis for the higher alkalinity concentration as expected according to the literature is that the alkalinity may has been supplemented by the solubilization of carbon dioxide formed due to organic matter degradation, in addition to the compensation caused by denitrification. Due to the alkaline pH, CO2 chemical equilibrium is shifted to bicarbonate increasing the system alkalinity (Equation 1 and 2) (DUBLEN e STEINHAUSER, 2011; KUNZ e MUKHTAR, 2016).

CO2 (g) + H2O ⇌ H2CO3 (aq)
H2CO3 (aq) ⇌ HCO3- (aq) + H+(aq) "

The equations are fine, but the conclusion that they add alkalinity is obviously wrong. It violates the Principle of the Conservation of Alkalinity:

Chemistry and the Aquarium: What is Alkalinity?

Randy provides an overview of alkalinity as to why it's important, how it's measured, and how can it be tested.

reefs.com

Alkalinity Facts
There are several facts about total alkalinity that follow directly from the definition. Unfortunately, some of these have been misunderstood by some hobby authors.

One of these facts is termed The Principle of Conservation of Alkalinity by Pankow (“Aquatic Chemistry Concepts”, 1991). He shows mathematically that the total alkalinity of a sample CANNOT be changed by adding or subtracting CO2. Unfortunately, there is an article available on line, which claims otherwise, and encourages people to “lower alkalinity” by adding CO2 in the form of seltzer water. This is simply incorrect.

Forgetting the math for the moment, it is easy to see how this must be the case. If carbonic acid is added to any aqueous sample with a measurable alkalinity, what can happen?

Well, the carbonic acid can release protons by reversing equations 1 and 2:

(5) H2CO3 ==> H+ + HCO3–

(6) HCO3– ==> H+ + CO3—

These protons can go on to reduce alkalinity by combining with something that is in the sample that provides alkalinity (carbonate, bicarbonate, borate, phosphate, etc). However, for every proton that leaves the carbonic acid and reduces alkalinity, a new bicarbonate or carbonate ion is formed that adds to alkalinity, and the net change in total alkalinity is exactly zero. The pH will change, and the speciation of the things contributing to alkalinity will change, but not the total alkalinity.

This is not true for strong acids, however. If you add hydrochloric, sulfuric or phosphoric acids (or any acid with a pKa lower than the carbonic acid endpoint), there will be a reduction in the alkalinity.

 

[Lasse]

Here is link 1 and 3 as PDF files and please comment their calculations
Page 12 in the pdf document named page12.pdf and page 3-4 in the document page 3_4

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

The first pdf says this:

"An additional factor favoring the use of denitrification is its ability to stabilize the buffering capacity of culture water. Acidification is often observed in nitrifying recirculating systems (e.g. Kaiser and Wheaton, 19831, where alkalinity decreases by 6.0-8.6 mg HCO; for each milligram of ammonium oxidized to nitrate (Sharma and Ahlert, 1977; Grady and Lim, 1980). However, release of hydroxyl ions by denitrification raises alkalinity; it was estimated that each mg of nitrate reduced to N, causes alkalinity to increase by 3.57 mg (Jeris and Owens, 1975). The overall effect of denitrification in stabilizing the pH in recirculating systems has been described (Otte and Rosenthal, 1979; Kaiser et al., 1989). "

While I do not have a good handle on the odd units of measure for alk they are using without seeing more detail in the original papers (which I cannot get past page 1; see below), they are showing what I am claiming: ammonia conversion to nitrate consumes alk and denitrification adds it back.

The main confusion (aside from strange units of measure for alk) may be coming that they write it as ammonium converted to nitrate, and then nitrate to N2.

First some conversion math.

1 mg ammonium becomes 3.44 mg nitrate

So they claim 1 mg ammonium (we'll come back to the ammonium ammonia issue) to nitrate decreases alk by 6.0-8.6 units of alk (let's call this an average of 7.3)

and that 1 mg of nitrate adds back 3.57 mg of alk when denitrified.

Thus, 1 mg of ammonium to 3.44 mg nitrate then denitrified removes 7.3 - 3.57 *3.44 = 7.3 - 12.2 = -4.9 units of alk

Ignoring the confusing units, this seems to roughly match my claim, taking into account that ammonium is not what we are concerned with being produced, it is ammonia!

Ammonia may rapidly get protonated, but that itself is an alk impacting process.

NH3 --> NH4+ + OH-

That adds alk. One cannot ignore that process and it must be added to the above equation. Of course, how much one adds back will depend on whether one is actually starting with ammonia (adds nothing more) or ammonium (adds 3.57 in their units?) and that is dictated by pH. the above numbers are measurements, not calculations from equations, and so one cannot assume that all ammonia/ammonium is in one form or the other. It is something in between.


The denitrification numbers are attributed to:

Jeris, J.S. and Owens, R.W., 1975. Pilot-scale, high rate biological denitrification. J. Water Pollut. Control Fed., 47: 2043-2057. Kaiser, G.E. and Wheaton.

https://www.jstor.org/stable/25038941

I cannot see past page 1, but they show the exact reaction that I assume at the bottom of page 1, which shows 1 unit of alk produced for each unit of nitrate consumed.

If you can get past page 1 of the Jeris paper above, we can perhaps see what numbers they actually showed and what the units of measure mean.

 

[Randy Holmes-Farley Verified Community Expert]

Second pdf also says what I claim:

5CH3COO-+ 8NO3- 3H+ --> 10HCO3- + 4N2 + 4H2O

It is made more complicated by using acetate instead of acetic acid or other neutral organic. Adding acetate will add alkalintiy, but using acetic acid will not:

5 CH3COOH --> 5 CH3COO- + 5 H+

Combining the two equations and subtracting 5 CH3COO- from both sides we get:

5 CH3COOH + 8NO3- 3H+ --> 10HCO3- + 4N2 + 4H2O + 5H+

The net change is 8 nitrates removed and the alk change is to add 8 units of alk (3 H+ consumed, 10 bicarbonate produced and 5 H+ produced).

hence, 1 nitrate produces 1 unit of alk when denitrified with a neutral organic material (ethnaol, acetic acid, methanol, sugar, etc, all give the same answer).

QED.

 

[Lasse]

I think the first paper use HCO3 as alkalinity - its an older European way of expressing alkalinity. From their text - my bold.

where alkalinity decreases by 6.0-8.6 mg HCO3 for each milligram of ammonium oxidized to nitrate (Sharma and Ahlert,
1977; Grady and Lim, 1980). However, release of hydroxyl ions by denitrification raises alkalinity; it was estimated that each mg of nitrate reduced to N, causes alkalinity to increase by 3.57 mg

The second paper state that - my bold

During nitrification, alkalinity decreases by approximately 7 mg CaCO3 for each mg of ammonia-N

(Alkalinity loss = 2 meq of alkalinity per mole NH4+ or 7.14 mg CaCO3/mg NH4+-N)

and - my bold

Each mg of nitrate-N reduced to N2 causes an alkalinity increase of 3.57 mg CaCO3

(Alkalinity gain = 1 meq of alkalinity per mole NO3 or 3.57 mg CaCO3/mg NO3-N)

IMO - this says that the alkalinity loss per mole NH4 (or mg NH4-N) is double the gain of alkalinity that you get in the denitrification process of the produced NO3 from the nitrification, IMO - its means that in a recirculation system with both nitrification and simultaneously denitrification (like an recirculated fish farm with denitrification) you will have a steady loss in alkalinity

What I have understand you before - you have state that the gain of alkalinity in the denitrification process will be exactly the same as the loss in the nitrification process.

Sincerely Lasse