Alkalinity for the Chemistry Challenged Reefer

[Daniel@R2R Verified Admin]

We see some reefers preferring high alk and some preferring low alk. But what exactly does alkalinity do in a reef tank?

I'll be the first to admit that my chemistry knowledge is pretty basic. I mean, I can defend myself in most basic hobby-level conversations, but there are a lot of people who talk chemistry that frankly are just way smarter than me, and even though I try my best to follow the explanations, I get lost in the weeds somewhere.

So, how would you explain alkalinity to someone who is "chemistry challenged"?

I'll go ahead and add the points that (I think) I know:

1. Alkalinity is one of the most essential dynamics of reef chemistry and is important to coral metabolism.
2. Stability is probably the most important factor when maintaining alk levels in a reef tank (your specific alk number is not as important as keeping whatever that number is from spiking or dipping).
3. Sharp changes in alkalinity is probably one of the biggest causes of tank crashes.
4. Alkalinity is not an element or even an actual "thing" but rather describes the acidity level of the water.
5. When deciding what alkalinity numbers to target, higher levels of nutrients permit higher levels of alkalinity (whereas lower level nutrient tanks should opt for lower levels of alk).

So...can we make this thread kind of a "Alkalinity for Dummies" kind of thread? Can you explain alkalinity for the chemistry challenged?

 

[Randy Holmes-Farley Verified Community Expert]

Simplest I can think of:

Corals and other calcifying organisms use bicarbonate from the water to deposit calcium carbonate skeletons.

Bicarbonate is quite hard to measure at home, so we use alkalinity as a surrogate measure to ensure there is enough present. Alkalinity is mostly bicarbonate.

 

[Daniel@R2R Verified Admin]

Simplest I can think of:

Corals and other calcifying organisms use bicarbonate from the water to deposit calcium carbonate skeletons.

Bicarbonate is quite hard to measure at home, so we use alkalinity as a surrogate measure to ensure there is enough present. Alkalinity is mostly bicarbonate.

Thanks Randy! Were the points I made above correct? Please correct anything I may have wrong.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy! Were the points I made above correct? Please correct anything I may have wrong.

I don't think #4 is quite right. Alkalinity (TA = total alkalinity) is not a single thing, but it is a clear set of things added together:

TA = [HCO3–] + 2[CO3—] + [B(OH)4–] + [OH–] + [Si(OH)3O–] + [MgOH+] + [HPO4—] + 2[PO4—] – [H+]

We happen to measure it all at once by dropping the pH to about 4 and seeing how much acid that takes since each of those takes up acid as the pH is lowered to that point. But total alkalinity is not really a measure of the acidity level of the water. pH does that.

https://www.reef2reef.com/ams/what-is-alkalinity.8/

 

[Daniel@R2R Verified Admin]

I don't think #4 is quite right. Alkalinity (TA = total alkalinity) is not a single thing, but it is a clear set of things added together:

TA = [HCO3–] + 2[CO3—] + [B(OH)4–] + [OH–] + [Si(OH)3O–] + [MgOH+] + [HPO4—] + 2[PO4—] – [H+]

We happen to measure it all at once by dropping the pH to about 4 and seeing how much acid that takes since each of those takes up acid as the pH is lowered to that point. But total alkalinity is not really a measure of the acidity level of the water. pH does that.

https://www.reef2reef.com/ams/what-is-alkalinity.8/

Thanks! That's a helpful clarification.

 

[Randy Holmes-Farley Verified Community Expert]

I'd also add a number 6; higher alkalinity can lead to faster calcification (skeletal growth) of many hard corals. The reason for #5 is presumably because the coral needs more nutrients to keep the tissue growing fast enough to cover faster growing skeletons of some corals, or risk getting 'burnt tips' which may be too thin of tissue on coral growing tips.

 

[bushdoc]

Often you see on this forum statements like “ your alkalinity is too low or too high” , but it is important to understand that it depends on your nutrients level as Daniel stated, but also what type of corals if any you grow, higher dKH needed for SPS/LPS, but not so much for gorgonians or soft corals or FOWLR.

 

[Miami Reef]

We happen to measure it all at once by dropping the pH to about 4 and seeing how much acid that takes since each of those takes up acid as the pH is lowered to that point.

What happens if you just recently added acid to lower the alkalinity prior, but you didn’t aerated well prior to testing. Will the alkalinity show lower than what it really is, since it will take less titration to lower the pH to 4?

 

[Randy Holmes-Farley Verified Community Expert]

What happens if you just recently added acid to lower the alkalinity prior, but you didn’t aerated well prior to testing. Will the alkalinity show lower than what it really is, since it will take less titration to lower the pH to 4?

If you add acid, the true alk immediately drops and the tank has substantially elevated CO2 and lower pH.

The measured alk will likely be close to the true alk. The true pH endpoint will shift a bit, and the test kit endpoint does not leading to a mismeasurement.

We have a pretty in depth discussion on that topic with some experts here, including Habib Sekha (owner of Salifert) and Chris Jury.

http://www.reefcentral.com/forums/showthread.php?t=2130613

 

[Miami Reef]

Thanks, Randy. :)

 

[taricha]

4. Alkalinity is not an element or even an actual "thing" but rather describes the acidity level of the water.

Another approach at this might be that it's sort of an inverse to acid - but not a high pH base - it's a buffer. Kind of like antacid (not that different from Tums - but in the water) - in that the Total Alk we measure is literally how much acid it takes to react with this buffer in our water. More Alk (buffer), the more acid it takes to destroy the buffer.

1. Alkalinity is one of the most essential dynamics of reef chemistry and is important to coral metabolism.

The sensitivity of coral biology to this parameter is probably because it reflects how close the water is to literally forming solid crystals out of the water.
These liquids form solids inside the bodies of coral animals - which is kind of a dramatic process if you think about it. And changing this parameter is changing how fast liquids turn into solid crystals inside the animal.

Maybe those explanations are helpful. Hopefully they aren't too wrong.

 

[Miami Reef]

@taricha read this (click on Randy‘s name to go to the original thread he posted it in)

I recommend the alk range for a few reasons, but mostly because that’s where reef tanks seem to do best.

Too high of alk is mostly a precipitation issue, and too low of alk may stress corals, especially in tanks where the pH is low too. That’s not a common combo in the ocean.

It seems corals can readily thrive in higher alk and that’s not too surprising, just like they can thrive with other needed nutrients higher than normal.

Corals have to actively work to take up carbonate/bicarbonate to make calcium carbonate, and they use active protein transporters in their membranes to accomplish that task.

Changes in alk make that harder or easier, and it takes substantial time for organisms to up or down regulate the number of such transporters. Thus, a sudden alk change may leave the coral not getting enough or being force fed too much until it makes transporter changes, and during that interim period, it may suffer as a consequence.

That summary is a substantial simplification of something that is not perfectly understood, but I think it conveys the gist of reality.

 

[Daniel@R2R Verified Admin]

Another approach at this might be that it's sort of an inverse to acid - but not a high pH base - it's a buffer. Kind of like antacid (not that different from Tums - but in the water) - in that the Total Alk we measure is literally how much acid it takes to react with this buffer in our water. More Alk (buffer), the more acid it takes to destroy the buffer.



The sensitivity of coral biology to this parameter is probably because it reflects how close the water is to literally forming solid crystals out of the water.
These liquids form solids inside the bodies of coral animals - which is kind of a dramatic process if you think about it. And changing this parameter is changing how fast liquids turn into solid crystals inside the animal.

Maybe those explanations are helpful. Hopefully they aren't too wrong.

Yes! Thank you!

 

[Borat]

It is important that your tank's alkalinity is higher than that of your neighbour Bob. So if he comes and boasts "..high alkalinity and ultra-rare SPS growing like weed.." - make sure your alkalinity is at least 50% higher than his.

 

[taricha]

@taricha read this (click on Randy‘s name to go to the original thread he posted it in)

yeah, my oversimplification that ignores coral's active role is way more wrong than Randy's. :)

 

[s70]

I have trouble with my alkalinity going down.
2.5 Nitrates
Phosphorus around 50
SPS/LPS
I have Kalkwasser running.

What are some potential causes of Alk going down?

Thanks

 

[Propane]

Does dosing ammonia lower alkalinity?

 

[Randy Holmes-Farley Verified Community Expert]

Does dosing ammonia lower alkalinity?

Depends on what exactly you dose, but lowering alk generally just means one is not dosing enough alk.

 

[Randy Holmes-Farley Verified Community Expert]

I have trouble with my alkalinity going down.
2.5 Nitrates
Phosphorus around 50
SPS/LPS
I have Kalkwasser running.

What are some potential causes of Alk going down?

Thanks

What is the alk?

How did you decide how much kalk to dose?

What is in the tank?

 

[Propane]

Depends on what exactly you dose, but lowering alk generally just means one is not dosing enough alk.

I thought I read somewhere that creating nitrates lowers alkalinity. I recently added 2 fish and when I stopped dosing ammonia my alk went up and then back down when I resumed ammonia dosing. I was wondering if there was any relation.