- What's the pH of your reef tank?
Is it 7.8?
8.5?
It probably changes throughout the day
and that leads to concerns about what effect
that pH change has on our corals.
I mean, does it make your Acropora less colorful?
Do SPS corals just grow slower?
Could low pH at night kill our corals?
Hi guys, and girls, I'm ReefMan.
And this video is all about that daily pH swing.
We'll be using a paper recently published
in "Coral Reefs" and it's titled
"Coral persistence
"despite extreme periodic pH fluctuations
"and a volcanically acidified Caribbean reef."
There's a link down below.
I encourage you to check it out.
It's a cool paper.
Natural reefs can sometimes undergo very big pH swings.
Think about reefs near volcanic vents.
These sea floor vents are not always thousands of feet deep
in the ocean.
And when they're shallow,
they're often found in areas
that would otherwise be a great habitat for coral.
Now I'm not talking about a vent
that's spewing out magma,
boiling hot water is going to kill just about everything.
I'm talking about gas vents,
and particularly gas vents that vent a large amount
of CO2-rich volcanic gas
just bubbling up constantly into the water.
So this paper is particularly studying a reef
in the Caribbean near St. Vincent and the Grenadines
and it's in the Caribbean Sea.
It has two large daily swings in pH due to a slack tide
and volcanic CO2 venting in the area.
The lowest pH on this reef during those swings was 6.54.
That is way lower than any of us
would ever consider running a reef tank.
That's a pH you might expect
to find inside a calcium reactor, not on a reef.
A high average pH, may be around eight or 8.2.
That's important to achieve.
The carbonite skeletons inside our stony coral are laid down
only in those high pH environments.
The coral itself is able to raise the pH even higher,
really close to its tissue,
and that causes the calcium to come out of solution.
And that's how stony corals actually build their skeleton.
If the ocean water pH is just too low,
that's not gonna happen
because corals can only raise it so much.
If the pH is even lower,
that skeleton will start to dissolve.
And for sure, 6.5 is in a dissolving range
where calcium carbonate cannot be saturated out
of the water.
In general, reefs in areas that have persistent drop
like that in pH tend to be populated
by a lotta algae and soft corals.
Corals that don't need
to lay down a calcium-based skeleton to survive.
But in this reef, in the Caribbean,
at least it's doing just fine.
Stony corals are growing,
if not maybe a little bit slower than average.
But it's key that the average pH is still fine.
Even on this reef,
there are just these frequent slack tides
that just cause a short term drop in the pH,
just like a nighttime on our reef aquarium.
Now I mentioned that they found pH levels as low as 6.54.
That's a level at which calcium in the water
will not be saturated anymore.
And that's going to outright prevent stony coral growth
because it's just impossible for the corals
to bring the calcium out of solution at that pH.
Even so, stony corals
like Orbicella, Porites, and Montastrea
were found growing in this area.
The pH on this reef is mostly around 8.1 on average,
and it does have regular drops down
to anywhere between, you know, 8.1 and 6.5 or so.
So that sounds an awful lot like our tanks
with even a larger pH swing that we would expect to see.
On wild reefs, this swing in pH can actually be a boon
for some Acropora growths.
One paper found that daytime boosts
in pH due to photosynthetic activity, things like that.
It seemed to actually speed up the growth
of some Acropora cervicornis populations.
So as long as your daytime pH recovers enough
that the average pH in your tank is at least eight or so,
it seems like you've got nothing to worry about
from a overall coral health perspective.
In reef tanks, it's not uncommon
to see low pH around 7.8
and a high pH around 8.4 during the day.
If you're using a calcium reactor,
you might never even get to 8.4.
In general, this is not something you
should worry too much about.
If you want to, you could dose kalkwasser
along with your calcium reactors effluent
to keep the tank's average pH higher,
but you're still gonna have that daily swing in pH.
And it's not something
that you should let really bother you.
It's okay.
Another tip here at the end,
be sure you have proper aeration
if you're facing a pH issue.
Sometimes it can be as simple
as just making sure you're getting enough air
into the water via surface movement
or a protein skimmer or something like that.
If possible, open a window in your house.
Sometimes our homes trap enough CO2
to impact your reef tank's pH.
Even cooking can change the pH of your tank.
The next time you're making a big family meal
for the holiday, check out your tanks pH afterwards.
I'll bet you you'd be surprised at how low it went.
So don't really fret all that much
when you see your nighttime pH down
in the high, mid 70s, high, mid sevens.
That's not too low a value, and it's not that bad.
Look at how your coral's doing.
Be holistic about it.
If they're happy, don't worry about it.
I hope you enjoyed the video.
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I post about once a week.
Be excellent to each other and party on, bye.