Question about alkalinity to Randy

[Miami Reef]

Hello Randy,

I have a few questions about alkalinity.

1. Why is an alk of 7-11dkh recommended if natural sea water is about 6.5dkh?

2. Can wild corals (acros) adapt to the high range even though they’ve adapted and evolved to be in lower alkalinity?

3. Why is 11dkh the limit? Why not higher? I’d like to understand how 11-12dkh became the limit.

Edit: bonus question:

4. why do alk spikes cause certain corals to die? What happens to the coral when alk quickly spikes?

 

[Jekyl]

@Randy Holmes-Farley

 

[shakacuz]

all very valid questions. following along

 

[Randy Holmes-Farley]

Hello Randy,

I have a few questions about alkalinity.

1. Why is an alk of 7-11dkh recommended if natural sea water is about 6.5dkh?

2. Can wild corals (acros) adapt to the high range even though they’ve adapted and evolved to be in lower alkalinity?

3. Why is 11dkh the limit? Why not higher? I’d like to understand how 11-12dkh became the limit.

Edit: bonus question:

4. why do alk spikes cause certain corals to die? What happens to the coral when alk quickly spikes?

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.

 

[Nanogeek815]

@Randy Holmes-Farley Is there any information or testing done to verify that the stress from an alk swing is not due to a resulting pH swing? Usually when alk moves, pH does as well.

Is there a good way to test this?

 

[Randy Holmes-Farley]

@Randy Holmes-Farley Is there any information or testing done to verify that the stress from an alk swing is not due to a resulting pH swing? Usually when alk moves, pH does as well.

Is there a good way to test this?

I’ve not seen anyone try to test this.

it is certainly possible to make alk swings with no pH change, and pH swings with no alk change, but it requires a fair amount of effort and how complicated it is depends on how long you want to maintain it.

A mix of bicarbonate and carbonate can be made to have no immediate pH change for any size alk boost. If you want the pH to not change subsequent to that dose and aeration, then one may need to alter the CO2 in the aerating air. Tricky, but possible.

A downward alk swing (or upward) is also possible to attain by water change, and careful aeration can match the pH before the change.

But the whole notion of pH stability becomes complicated if the time frame is long enough to include day night cycles.