Are alkalinity swings a problem for corals?

[bakbay]

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!

Same thing as balling method to replenish Alk & Ca (+Mg if you like). I love CaRx and will never go back to dosing due to the maintenance aspects. I just need to replace CO2 and media every 11-12mos. Beyond that — it’s pretty much autopilot.

Anyway, I screwed up this time when I added more media. To prevent overfilling the unit, I scooped out the water but instead of throwing it away, I dumped the highly concentrated solution into the sump, which quickly raised Alk/Ca. Worse - I turned the CO2 back online and went to bed — with more media, more Alk/Ca! Note to self: don’t do this again next year!

 

[gbroadbridge]

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!

But of course, significant Alk swings will not affect coral in the time frames being mentioned here.

Expecting to see the effect within days of the change is not really a reliable indicator.

Where I have seen damage attibuted to Alk swings, it usually manifests weeks to months later, when all other parameters remain consistent.

 

[bakbay]

But of course, significant Alk swings will not affect coral in the time frames being mentioned here.

Expecting to see the effect within days of the change is not really a reliable indicator.

Where I have seen damage attibuted to Alk swings, it usually manifests weeks to months later, when all other parameters remain consistent.

Ok - thanks for the heads up, will report if anything changes in a few weeks/months. I don’t change much / if anything to this tank.

 

[IntrinsicReef]

But of course, significant Alk swings will not affect coral in the time frames being mentioned here.

Expecting to see the effect within days of the change is not really a reliable indicator.

Where I have seen damage attibuted to Alk swings, it usually manifests weeks to months later, when all other parameters remain consistent.

If it happens weeks to months later ( a very broad timeline) how are you sure it was caused by the previous alk spike. And what type of damage should we look for?

 

[IntrinsicReef]

Same thing as balling method to replenish Alk & Ca (+Mg if you like). I love CaRx and will never go back to dosing due to the maintenance aspects. I just need to replace CO2 and media every 11-12mos. Beyond that — it’s pretty much autopilot.

Anyway, I screwed up this time when I added more media. To prevent overfilling the unit, I scooped out the water but instead of throwing it away, I dumped the highly concentrated solution into the sump, which quickly raised Alk/Ca. Worse - I turned the CO2 back online and went to bed — with more media, more Alk/Ca! Note to self: don’t do this again next year!

I have run calcium reactors on several systems over the years and they have been finicky for me. Especially on client tanks that I only see once every week or two. I have seen some amazing systems run calcium reactors but I have just found dosers more consistent for my needs.

 

[gbroadbridge]

If it happens weeks to months later ( a very broad timeline) how are you sure it was caused by the previous alk spike. And what type of damage should we look for?

Well, let's say a tank that has been perfectly stable for a long time (over 12 months) which suddenly due to doser or CaRx fault experiences a large Alk swing from 7 to 12dkh which is then corrected rapidly (within 24 hours) and then 4-10 weeks later experiences a STN event or other coral deterioration.

If this happened only once, I would consider that something else may have caused the deterioration.

When I've seen it happen a number of times across a few disparate systems, I start to believe the two events may be related.

Of course it could all simply be coincidence.

I don't know whether anyone has actually had the time to conduct the experiment in controlled conditions.

 

[IntrinsicReef]

Well, let's say a tank that has been perfectly stable for a long time (over 12 months) which suddenly due to doser or CaRx fault experiences a large Alk swing from 7 to 12dkh which is then corrected rapidly (within 24 hours) and then 4-10 weeks later experiences a STN event or other coral deterioration.

If this happened only once, I would consider that something else may have caused the deterioration.

When I've seen it happen a number of times across a few disparate systems, I start to believe the two events may be related.

Of course it could all simply be coincidence.

I don't know whether anyone has actually had the time to conduct the experiment in controlled conditions.

-IMO 4-10 weeks is too broad a time a timelime to be helpful. I don't think anyone can say with any certainty that coral damage was caused by an alk spike 1 to 2.5 months earlier. Most Acropora for example grow observable tissue within 14 days. Possibly, damage done wouldn't be seen until up to two weeks later, but as fast as corals react to negative conditions this is unlikely to me.
-Reef tanks aren't "perfectly stable". They are ever changing closed systems that fluctuate with our inputs, outputs and animal growth. Even the most experienced reef keepers deal with parameter fluctuations over the course of a year. And all of those parameters are intertwined with each other.
-I think if you are seeing STN in corals, you would do well to look at other possible causes besides an alk spike months earlier.

 

[Borat]

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.

the "corals" referred to here - are these the likes of kenya tree?

 

[Borat]

..also I like the idea/spirit of this discussion - "Chemical experiments to create battle-hardened marine pets"!

 

[IntrinsicReef]

..also I like the idea/spirit of this discussion - "Chemical experiments to create battle-hardened marine pets"!

Hey Borat! Maybe you've heard of the US Navy's Marine Mammal Program. Well, this is the Civil Scleractinian Program. Coral colors so intense they will cause irreparable ocular damage to our enemies.

 

[Hairy Tee]

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.

I agree wholeheartedly! I've always had freshwater tanks (still have a 125g with 12 gorgeous Altum angel fish. One of which is wild caught from the Amazon!), however, two months ago I got the bug and set up my Biocube 32 to be a saltwater reef tank. I'm loving it so much I just bought an Innovative Marine SR2 80 Pro. The whole alkalinity thing is driving nuts with so much information on the internet. I used Instant Ocean Reef salt for the Biocube and decided to go with Tropic Marin Pro salt for the 80 gallon. I did this primarily because I want to do auto water changes and it holds up better when storing it for several weeks plus I think it is a better salt mix. The alkalinity on my Biocube is 10 dkh but my concern is Tropic Marin Pro is at 7 dkh so I am trying to decide if I want to just let the alkalinity ride at 7 dkh for both the Biocube 32 and the IM 80 gallon or do I dose Soda Ash to increase the alkalinity. I've been searching all over the internet and can't get a definitive answer! Some say 7 dkh is fine and others say it needs to be closer to 10 dkh! Not sure which way I am going to go. LOL

 

[IntrinsicReef]

I agree wholeheartedly! I've always had freshwater tanks (still have a 125g with 12 gorgeous Altum angel fish. One of which is wild caught from the Amazon!), however, two months ago I got the bug and set up my Biocube 32 to be a saltwater reef tank. I'm loving it so much I just bought an Innovative Marine SR2 80 Pro. The whole alkalinity thing is driving nuts with so much information on the internet. I used Instant Ocean Reef salt for the Biocube and decided to go with Tropic Marin Pro salt for the 80 gallon. I did this primarily because I want to do auto water changes and it holds up better when storing it for several weeks plus I think it is a better salt mix. The alkalinity on my Biocube is 10 dkh but my concern is Tropic Marin Pro is at 7 dkh so I am trying to decide if I want to just let the alkalinity ride at 7 dkh for both the Biocube 32 and the IM 80 gallon or do I dose Soda Ash to increase the alkalinity. I've been searching all over the internet and can't get a definitive answer! Some say 7 dkh is fine and others say it needs to be closer to 10 dkh! Not sure which way I am going to go. LOL

Salt brand is another factor that I think people put too much weight on. Many people have success with both salts and both alkalinity levels. I use IO Reef Crystals because of availability and economy. Tropic Marin makes a great program that people use to create beautiful reef tanks. Their Balling method is legendary and I do my own version of it. I think anyone who is undecided about a method to follow would do well just to adhere to their Balling Method.

I tend to keep alkalinity at a higher level to help buffer pH. I have found keeping pH at ocean averages of 8.3 more important than a certain alkalinity level. I usually have to keep alkalinity higher to counter the elevated CO2 trapped in our indoor air. I like to dose soda ash at night to replace carbonates absorbed by corals and to level out the natural daily pH swing.

 

[Randy Holmes-Farley]

I've been searching all over the internet and can't get a definitive answer! Some say 7 dkh is fine and others say it needs to be closer to 10 dkh! Not sure which way I am going to go. LOL

To whether you should raise the alk?

You cannot find an answer to that any more than you can find a definitive answer on what type of car is best.

There are a number of things that go into choosing an alk target, and what you end up selecting will depend on your system, your goals, and your tank inhabitants.

Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley

[note: edited on 5/29/2022 to update the nitrate and phosphate sections with higher recommended levels.] One of the main roles of an aquarist with a coral reef aquarium is to ensure that the conditions are right for their tank inhabitants. There are many different attributes of the aquarium...

www.reef2reef.com

Alkalinity

Like calcium, many corals also use "alkalinity" to form their skeletons, which are composed primarily of calcium carbonate. It is generally believed that corals take up bicarbonate, convert it into carbonate, and then use that carbonate to form calcium carbonate skeletons. That conversion process is shown as:

HCO3- → CO3-- + H+

Bicarbonate → Carbonate + proton (which is released from the coral)

To ensure that corals have an adequate supply of bicarbonate for calcification, aquarists could just measure bicarbonate directly. Designing a test kit for bicarbonate, however, is somewhat more complicated than for alkalinity. Consequently, the use of alkalinity as a surrogate measure for bicarbonate is deeply entrenched in the reef aquarium hobby.

So, what is alkalinity? Alkalinity in a marine aquarium is simply a measure of the amount of acid (H+) required to reduce the pH to about 4.5, where all bicarbonate is converted into carbonic acid as follows:

HCO3- + H+ → H2CO3

The amount of acid needed is equal to the amount of bicarbonate present, so when performing an alkalinity titration with a test kit, you are counting the number of bicarbonate ions present. It is not, however, quite that simple since some other ions also take up acid during the titration. Both borate and carbonate also contribute to the measurement of alkalinity, but the bicarbonate dominates these other ions since they are generally lower in concentration than bicarbonate. So knowing the total alkalinity is akin to, but not exactly the same as, knowing how much bicarbonate is available to corals. In any case, total alkalinity is the standard that aquarists use for this purpose.

Unlike the calcium concentration, it is widely believed that certain organisms calcify more quickly at alkalinity levels higher than those in normal seawater. This result has also been demonstrated in the scientific literature, which has shown that adding bicarbonate to seawater increases the rate of calcification in some corals. Uptake of bicarbonate can consequently become rate limiting in many corals. This may be partly due to the fact that the external bicarbonate concentration is not large to begin with (relative to, for example, the calcium concentration, which is effectively about 5 times higher).

For these reasons, alkalinity maintenance is a critical aspect of coral reef aquarium husbandry. In the absence of supplementation, alkalinity will rapidly drop as corals use up much of what is present in seawater. Water changes are not usually sufficient to maintain alkalinity unless there is very little calcification taking place. Most reef aquarists try to maintain alkalinity at levels at or slightly above those of normal seawater, although exactly what levels different aquarists target depends a bit on the goals of their aquaria.

Interestingly, because some corals may calcify faster at higher alkalinity levels, and because the abiotic (nonbiological) precipitation of calcium carbonate on heaters and pumps also rises as alkalinity rises, the demand for alkalinity (and calcium) rises as the alkalinity rises. So an aquarist generally must dose more calcium and alkalinity EVERY DAY to maintain a higher alkalinity (say, 11 dKH) than to maintain 7 dKH. It is not just a one-time boost that is needed to make up that difference. In fact, calcification gets so slow as the alkalinity drops below 6 dKH that reef aquaria rarely get much below that point, even with no dosing: natural calcification has nearly stopped at that level.

In general, I suggest that aquarists maintain alkalinity between about 7-11 dKH (2.5 and 4 meq/L; 125-200 ppm CaCO3 equivalents). Many aquarists growing SPS corals and using Ultra Low Nutrient Systems (ULNS) have found that the corals suffer from burnt tips if the alkalinity is too high or changes too much. It is not at all clear why this is the case, but such aquaria are better served by alkalinity in the 7-8 dKH range.

As mentioned above, alkalinity levels above those in natural seawater increase the abiotic precipitation of calcium carbonate on warm objects such as heaters and pump impellers, or sometimes even in sand beds. This precipitation not only wastes calcium and alkalinity that aquarists are carefully adding, but it also increases equipment maintenance requirements and can damage a sand bed, hardening it into a chunk of limestone. When elevated alkalinity is driving this precipitation, it can also depress the calcium level. An excessively high alkalinity level can therefore create undesirable consequences.

I suggest that aquarists use a balanced calcium and alkalinity additive system of some sort for routine maintenance. The most popular of these balanced methods include limewater (kalkwasser), calcium carbonate/carbon dioxide reactors, and the two-part/three part additive systems.

For rapid alkalinity corrections, aquarists can simply use baking soda (sodium bicarbonate) or washing soda (sodium carbonate; baked baking soda) to good effect. The latter raises pH as well as alkalinity while the former has a very small pH lowering effect. Mixtures can also be used, and are what many hobby chemical supply companies sell as buffers. Most often, sodium carbonate is preferred, however, since most tanks can be helped by a pH boost.