Are alkalinity swings a problem for corals?

[IntrinsicReef]

I have seen alk swings blamed for every type of coral malady. Especially " burnt tips" and STN/ RTN. Personally, I haven't seen these issues. I monitor reef aquariums by pH and have systems ranging ranging 7 to 12 dkh depending on fish load and ambient Co2. If a doser goes out and the pH drops, I have no issues making a corrective dose and making a sudden adjustment from 7 to 10dkh. I have recently heard many anecdotes from experienced aquarists state that they made similar corrective adjustments with no effect on the coral. So maybe the concensus towards alk swings is changing?
My question is: is there a chemical reason why an alk swing would harm corals?
People are leary of doing water changes with certain salts because of high alk. Personally, I have never seen a coral skip a beat doing a water change with salt at 11dkh, even if the system is running at 7dkh. I understand that some corals are accustomed to captive conditions and more tolerant than others. I just feel like this topic is confusing newer aquarists that are chasing alk stability and I'm haven't heard a good reason why.

 

[Randy Holmes-Farley]

There is certainly a hand waving argument about how alk changes might negatively impact corals.

Corals have to actively work to take up bicarbonate and/or carbonate. They do this with transporter proteins that use energy of some sort (not sure if it is ion gradient energy across cell membranes or direct chemical energy use such as ATP).

How hard they have to work to accomplish this depends on multiple factors such as pH and bicarbonate/carbonate concentration.

Organisms adjust to the availability of essential molecules they take up by regulating the number of these transporters that are active.

I do not know how fast corals are able to do such regulation, but in the wild alk rarely varies so they would not have needed a rapidly responsive regulation system.

If alk rises or falls faster than they can regulate, it causes an imbalance of too much or too little bicarbonate inside of them. If that imbalance is significant enough and lasts long enough, I can readily imagine it stresses corals.

 

[IntrinsicReef]

There is certainly a hand waving argument about how alk changes might negatively impact corals.

Corals have to actively work to take up bicarbonate and/or carbonate. They do this with transporter proteins that use energy of some sort (not sure if it is ion gradient energy across cell membranes or direct chemical energy use such as ATP).

How hard they have to work to accomplish this depends on multiple factors such as pH and bicarbonate/carbonate concentration.

Organisms adjust to the availability of essential molecules they take up by regulating the number of these transporters that are active.

I do not know how fast corals are able to do such regulation, but in the wild alk rarely varies so they would not have needed a rapidly responsive regulation system.

If alk rises or falls faster than they can regulate, it causes an imbalance of too much or too little bicarbonate inside of them. If that imbalance is significant enough and lasts long enough, I can readily imagine it stresses corals.

Thank you for the very interesting reply that immediately sent my mind into drawing inferences. So potentially, repeated alkalinity fluctuations can tax corals by forcing them to expend energy on adjusting these transporters instead of using energy on other necessary functions? Whereas a single "large" swing might just result in a reduction of growth for a coral that has it's energy needs met? This is consistent with anecdotes I've heard stating that coral's carbonate consumption (growth rate) was temporarily reduced following an alk swing.

 

[bakbay]

Interesting and very timely. I’ve had to replace the CaRx media two days ago and inadvertently spiked Alk from 8.4 to 11.5 dKH! pH was within range the whole time and so far — all corals (including sensitive acros) have been unaffected. I’ve turned off the CaRx and Alk settled to 10 today. Will let things come down on their own…

(knock on e-wood) Hope to not wake up tomorrow with acros RTN’ing

 

[IntrinsicReef]

Interesting and very timely. I’ve had to replace the CaRx media two days ago and inadvertently spiked Alk from 8.4 to 11.5 dKH! pH was within range the whole time and so far — all corals (including sensitive acros) have been unaffected. I’ve turned off the CaRx and Alk settled to 10 today. Will let things come down on their own…

(knock on e-wood) Hope to not wake up tomorrow with acros RTN’ing

Please keep me updated on any observations you make. If it were me, I would let it come back down on it's own as well. Who knows, maybe you will target a different alkalinity after this experience.

 

[dschuffert]

I have found that an alkalinity swing that is too big can harm corals. I use an Alkatronic connected to a Dosetronic for measuring and dosing the proper amounts of Red Sea dKH. I keep my alkalinity range between 9.5 and 10.

 

[IntrinsicReef]

I have found that an alkalinity swing that is too big can harm corals. I use an Alkatronic connected to a Dosetronic for measuring and dosing the proper amounts of Red Sea dKH. I keep my alkalinity range between 9.5 and 10.

I tend to stay in the 9.5-10 dkh range as well to keep pH at a 8.2-8.3 average. If I run the dkh lower, I usually struggle to keep the pH at the natural ocean average. What specific harm have you seen to corals and what was your measured swing over what time period?

 

[rtparty]

I’ve yet to see any evidence that alk swings hurt corals. Just theories and anecdotal evidence at best. I’ve watched dozens of tanks over the years spike alkalinity 4, 5, 6dkh in a matter of minutes (or hours) if a dosing pump fails on.

I’ve had my own tanks swing 2dkh numerous times over the years. Never seen corals suffer from it if they are healthy.

My evidence is anecdotal as well so it’s a lot of he said she said back and forth on who to believe

 

[IntrinsicReef]

I’ve yet to see any evidence that alk swings hurt corals. Just theories and anecdotal evidence at best. I’ve watched dozens of tanks over the years spike alkalinity 4, 5, 6dkh in a matter of minutes (or hours) if a dosing pump fails on.

I’ve had my own tanks swing 2dkh numerous times over the years. Never seen corals suffer from it if they are healthy.

My evidence is anecdotal as well so it’s a lot of he said she said back and forth on who to believe

Your experiences mirror mine exactly. But as you said, I just have my empirical observations and can't relay much more than my anecdotes. I am thankful for Randy chiming in with a scientific opinion. Maybe it causes stress that can be cumulative with other stress factors. Maybe certain techniques I employ make corals less susceptible to alk swing damage. I have no idea. That is why I am curious to hear people's observations.

 

[bakbay]

My SPS-dominant tank consumes ~1.5dKH daily; but 2 days ago, it spiked by 2x. That’s the first in 3 years. I usually run at 8-8.5 dKH and it’s fairly stable with the CaRx.

Another factor here is nutrient level? My NO3/PO4 is 25/.18, respectively. Higher nutrient can tolerate higher alk?

 

[bakbay]

I tend to stay in the 9.5-10 dkh range as well to keep pH at a 8.2-8.3 average. If I run the dkh lower, I usually struggle to keep the pH at the natural ocean average. What specific harm have you seen to corals and what was your measured swing over what time period?

I’ve found that lower alk yielded better coloration while higher alk yielded better growth in my tank. 8-8.5 gives me some wiggle room should things swing in either direction.

 

[Miami Reef]

I’ve found that lower alk yielded better coloration while higher alk yielded better growth in my tank. 8-8.5 gives me some wiggle room should things swing in either direction.

Interesting observation. I’ve heard people say this a lot, but alkalinity doesn’t directly influence coloration. Could it be that you ran lower nutrients with the lower alkalinity?

 

[IntrinsicReef]

Higher nutrient can tolerate higher alk?

I have heard people say this but it hasn't been my experience. I carbon dose my system at home that stays at about 10dkh, and have to dose Nitrogen and feed Reef Roids every other day to keep detectable NO3 and PO4. I have toyed with alkalinity quite a bit in this tank and haven't seen any ill effects from 2-3dkh swings. I don't repeatedly have swings because I run 2 part and Kalk on dosers, but I have made some major adjustments with no observable effect on the corals.

 

[bakbay]

Interesting observation. I’ve heard people say this a lot, but alkalinity doesn’t directly influence coloration. Could it be that you ran lower nutrients with the lower alkalinity?

My nutrient is pretty stable (on the “higher” side) while the thing that I can control is alk (by dialing more/less CO2). The best color combo for me is alk in the high 7, low 8… Perhaps there are other things I don’t / can’t see but that has been my anecdotal observation.

 

[Waters]

I wonder about the affects of ALK swings on acros every time I introduce a new frag from another tank (with a different ALK level) without acclimating. Doesn't ever seem to negatively impact the new frag?

 

[IntrinsicReef]

I wonder about the affects of ALK swings on acros every time I introduce a new frag from another tank (with a different ALK level) without acclimating. Doesn't ever seem to negatively impact the new frag?

That is a good point. I stopped acclimating corals over a decade ago but still acclimate fish and inverts. I buy aquacultured corals that have been grown in 8dkh ( multiple generations of parent colonies as well), and add them to a tank with 10dkh and they don't skip a beat.

 

[jda]

I my general experience, stonies can handle an alk swing, but not so much alk swings.

Twice in one year, I let my co2 bottle run out and my tank alk went into the 4s. I added baking soda to get back to 6.8 all at once. Everything was fine. The rest of the year, the alk was between 6.6 and 7.4 with only steady rises or declines that the CaRx added. However, 4.5 to 6.8 is still less than 8 to 12. I would not want to do any of these very often.

I also feel that alk swings get blamed for a lot of other things that could get messed up when this happens since nearly everybody has a test kit for Alk.

 

[IntrinsicReef]

I my general experience, stonies can handle an alk swing, but not so much alk swings.

Twice in one year, I let my co2 bottle run out and my tank alk went into the 4s. I added baking soda to get back to 6.8 all at once. Everything was fine. The rest of the year, the alk was between 6.6 and 7.4 with only steady rises or declines that the CaRx added. However, 4.5 to 6.8 is still less than 8 to 12. I would not want to do any of these very often.

I also feel that alk swings get blamed for a lot of other things that could get messed up when this happens since nearly everybody has a test kit for Alk.

I agree that alk swings get blamed too often. They have become the whipping boy of coral ailments. I don't think that is healthy for our hobby when people blame alk swings and don't investigate what could really be the issue. Also, it makes me cringe to see hobbyists put so much weight on alk swings when advising/ troubleshooting for new hobbyists.

That is interesting about the test kits. It is an easy test and might be the first thing people grab when something looks off.

 

[bakbay]

Ok — I went from 8.4 to 11.5, back to 8.4 in 2 days (Sun - Tue). So far, no impact. I’m turning the CaRx back online tonight. It gave me a scare tbh since this was my first time going up by 3dKH!

 

[IntrinsicReef]

Ok — I went from 8.4 to 11.5, back to 8.4 in 2 days (Sun - Tue). So far, no impact. I’m turning the CaRx back online tonight. It gave me a scare tbh since this was my first time going up by 3dKH!

Thank you for the update! I was curious because I don't use calcium reactors on any of my systems anymore. I didn't know if there were any factors that were different with CaRX than Balling method. Glad to hear everything is fine!