How to balance Ca/Alk in the reef aquarium?

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After reading:


Here are my takeaways:
  • For most practical purposes, Ca and Alk are consumed equally.
  • However, "...the demand for calcium and alkalinity may not be precisely balanced at 20 ppm calcium per 1 meq/l of alkalinity..."
  • The biggest impact to balance will mostly depend on the uptake of Mag/Stro in the formation of coral which will differ in each tank.
  • "According to the ESV website, the two-part system B-ionic has a balance of 19.3 ppm calcium per 1 meq/L of alkalinity."
Let's assume that my tank is in line with ESV's predicted balance but I am dosing perfectly balanced Alk/Ca. So since my tank is consuming 1.4dKH a day (Kalk plus AFR), I would be seeing an imbalance of Ca of 0.35 per day (i.e calcium increasing). After 30 days, an increase of 10.5ppm. After 60 days, an increase of 21ppm. After 90 days, an increase of 31.5ppm. After 180 days, an increase of 63ppm.

My ASW has a dKH of 7.5ish and a Ca level of 450ppm. So after 180 days, the tank would be about 510ppm and in my opinion in need of adjustment.

A couple of questions:
  1. How does one best lower Ca? (Larger water changes with a lower Ca ASW works, but I'm not interested in large water changes or changing up my salts)
  2. Should Ca be corrected before one gets to 500ish? Is there a benefit to correcting earlier?
  3. Can you let the tank auto-correct through a precipitation event if you are auto-dosing Alk?
  4. Ca testing is notoriously prone to error, but can one be successful using Ca instead of Alk for dosing? If so how? Can it be automated?
 

Randy Holmes-Farley

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A couple of questions:
  1. How does one best lower Ca? (Larger water changes with a lower Ca ASW works, but I'm not interested in large water changes or changing up my salts)
  2. Should Ca be corrected before one gets to 500ish? Is there a benefit to correcting earlier?
  3. Can you let the tank auto-correct through a precipitation event if you are auto-dosing Alk?
  4. Ca testing is notoriously prone to error, but can one be successful using Ca instead of Alk for dosing? If so how? Can it be automated?

There's really no way to lower calcium except water changes or letting calcium carbonate be formed and not replace the calcium.

I do not think there is any issue with calcium up to 550 ppm or so.

Only drawback that I am aware of to high calcium is increased abiotic precipitation, but the effect is much smaller than a pH or alk rise.

Folks using Al for Reef are often using calcium for dosing rather than alk. It is much cruder and more prone to errors, but theoretically can work and Tropic Marin (Lou) recommends it.
 

blasterman

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I disagree with big chunks of the article but you are on the right path.

Its yet another example of assuming the reef keeping universe revolves around big, mature SPS tanks with lots of fast growing colonies. This is not the case of most tanks and alk and calcium are more frequently not in balance.

If using an all in one product the only way to work it is solve for calcium and supplement with alk (baking soda). If your alk / calcium consumption isn't consistent in the first place dosing pumps will just make the problem worse. Manually dosing baking soda using a reef calculator is easy and bullet proof.

So, here we are in the inevitable high calcium scenario. Calcium at 500 isn't that big a deal and if you have stony corals it will slowly lower. Water changes will help, but salt mixes contain calcium and the math tells you there will be a lot of wasted water.

This is where I differ with randy a bit. Im not a fan of sky high calcium, and even while it doesn't bother SPS ive not found it makes them grow faster and have seen high calcium levels irritate large zoas and softies. Even BRS admitted when they tested high calcium/alk levels for better SPS growth it was likely the high alk producing results...and I agree.
 
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Randy Holmes-Farley

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I disagree with big chunks of the article but you are on the right path.

Its yet another example of assuming the reef keeping universe revolves around big, mature SPS tanks with lots of fast growing colonies. This is not the case of most tanks and alk and calcium are more frequently not in balance.

I've heard you suggest this many times, and I am not averse to incorporating new processes into an updated version of that article if they are real, but do you have any specific process in mind that depletes either alkalinity or calcium that is not mentioned there?
 
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There's really no way to lower calcium except water changes or letting calcium carbonate be formed and not replace the calcium.

I do not think there is any issue with calcium up to 550 ppm or so.

Only drawback that I am aware of to high calcium is increased abiotic precipitation, but the effect is much smaller than a pH or alk rise.

Folks using Al for Reef are often using calcium for dosing rather than alk. It is much cruder and more prone to errors, but theoretically can work and Tropic Marin (Lou) recommends it.

So maybe, a reasonable approach would be to incorporate or switch to two-part instead of AFR. Monitor Ca and when it's consistently high, turn off AFR and/or Ca portion of two-part for a specific dosage amount to bring the tank back into a better balance.
 
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I disagree with big chunks of the article but you are on the right path.

Its yet another example of assuming the reef keeping universe revolves around big, mature SPS tanks with lots of fast growing colonies. This is not the case of most tanks and alk and calcium are more frequently not in balance.

I've heard a lot of anecdotal and apocryphal examples of this, but nothing scientificly backed.

My bet is that most of these are due to inaccurate Ca measurements. My Hanna Ca Tester is in my opinion +/- 20ppm. I can take two consecutive readings and get large differences.

A 20ppm differences is equal to a 2.8dKH swing. (If I have my math right)
 

taricha

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My bet is that most of these are due to inaccurate Ca measurements. My Hanna Ca Tester is in my opinion +/- 20ppm. I can take two consecutive readings and get large differences.
I think that's the right interpretation.
I was convinced from tests that my Alk was depleting faster than Ca, because I had a tank full "weird" non-sps things: gorgs, softies, big plating sponges.
Then I actually measured Ca and Alk daily for 30 days to average out all the errors and nail down the rates of each....
I calc'd 0.74dkH and 5.0ppm Ca per day. So, within test error of balanced ratios.

So after a month i can confirm really there is no value in testing Ca daily. All that calculating Ca daily consumption independent of Alk tells me is exactly the same thing that Alk consumption tells me - just with less accuracy.
I mean, I guess that was expected, but I thought that possibly between corals, gorgs, sponges, diatoms, mollusks, algae, abiotic precipitation etc - that it was possible something somewhere consumed more of either Ca or Alk than balanced ratios.
It just doesn't happen though. They all calcify in basically the same way. And Ca/Alk always move together.
Good to know for certain.
 
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I've heard you suggest this many times, and I am not averse to incorporating new processes into an updated version of that article if they are real, but do you have any specific process in mind that depletes either alkalinity or calcium that is not mentioned there?

@Randy Holmes-Farley Another thought here...

I wonder if the perceived unbalanced Alk consumption is due to CO2 swings?

For most tanks, the light cycle triggers photosynthetic organisms to consume CO2. Reducing CO2 in the tank not only increases pH but decreases Alkalinity.

Say we start at 700matm and 8.1pH NBS --> 8.6dKH

We go to 400matm and 8.2pH NBS --> 6.6dKH

A drop of 2dKH.

Again, I might be thinking about this in the wrong way...
 

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There's really no way to lower calcium except water changes or letting calcium carbonate be formed and not replace the calcium.

I do not think there is any issue with calcium up to 550 ppm or so.

Only drawback that I am aware of to high calcium is increased abiotic precipitation, but the effect is much smaller than a pH or alk rise.

Folks using Al for Reef are often using calcium for dosing rather than alk. It is much cruder and more prone to errors, but theoretically can work and Tropic Marin (Lou) recommends it.
Don’t calcium and alk have an inverse relationship?

Without elevated magnesium or phosphate, wouldn’t 500ppm calcium cause alk/pH drops?
 
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Don’t calcium and alk have an inverse relationship?

Without elevated magnesium or phosphate, wouldn’t 500ppm calcium cause alk/pH drops?

Not that I'm aware of.

What I think you are referring to is when one raises Alk and/or Ca too high which will result in an abiotic CaCO3 precipitation event which would consume Ca/Alk equally.
 
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Randy Holmes-Farley

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Don’t calcium and alk have an inverse relationship?

Without elevated magnesium or phosphate, wouldn’t 500ppm calcium cause alk/pH drops?

Somewhat related, but definitely not strictly inversely and 500 ppm calcium is not a significant "cause" of low alk or pH at normal magnesium.

The tendency to be inversely related is way exaggerated by false analogies in the hobby (like one crazy analogy of marbles in a bowl).

This article covers these issues in detail:


In general, pH and alkalinity are much bigger drivers of precipitation than is slightly elevated calcium.

from the article;

Combining these various factors, here are some combinations of calcium, alkalinity, and pH that have equal supersaturation with respect to aragonite:
saturation index = 1 (risky: dissolution of aragonite begins here)
pH = 7.7pH = 8.2
Calcium = 410 ppmCalcium = 340 ppm
Alkalinity = 2.5 meq/LAlkalinity = 1.0 meq/L
saturation index = 3 (typical of normal seawater)
pH = 8.2pH = 8.0pH = 8.4
Calcium = 410 ppmCalcium = 410 ppmCalcium = 260 ppm
Alkalinity = 2.5 meq/LAlkalinity = 4.0 meq/LAlkalinity = 2.5 meq/L
saturation index = 6 (non-biological precipitation is more likely)
pH = 8.2pH = 8.2
Calcium = 410 ppmCalcium = 820 ppm
Alkalinity = 5.0 meq/LAlkalinity = 2.5 meq/L
pH = 8.0pH = 8.7
Calcium = 410 ppmCalcium = 410 ppm
Alkalinity = 8.0 meq/LAlkalinity = 2.5 meq/L
pH = 8.45
Calcium = 410 ppm
Alkalinity = 4.2 meq/L
 

blasterman

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I've heard a lot of anecdotal and apocryphal examples of this, but nothing scientificly backed.

My bet is that most of these are due to inaccurate Ca measurements. My Hanna Ca Tester is in my opinion +/- 20ppm. I can take two consecutive readings and get large differences.

A 20ppm differences is equal to a 2.8dKH swing. (If I have my math right)

Yeah....like a dozen threads a week from somebody seeing their alk drop 2 dKH per day while their calcium stays the same.

Yep...they are hallucinating because they don't have a scientific basis.

Alk and calcium are not locked in a fixed ratio in captive tanks unless the calcifying organisms, aka large clams or rapidly growing SPS significantly outstrips the biological processes consuming alk, nitrate producing bacteria, etc. For many of not most reefers this is not the case. Some guy with a couple frags in his tank and a nitrate level of 30 isn't going to have anywhere close to a consistent ratio of calcium to alk consumption and for you to push it is both ignorant and detrimental.
 
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Yeah....like a dozen threads a week from somebody seeing their alk drop 2 dKH per day while their calcium stays the same.

Yep...they are hallucinating because they don't have a scientific basis.

Alk and calcium are not locked in a fixed ratio in captive tanks unless the calcifying organisms, aka large clams or rapidly growing SPS significantly outstrips the biological processes consuming alk, nitrate producing bacteria, etc. For many of not most reefers this is not the case. Some guy with a couple frags in his tank and a nitrate level of 30 isn't going to have anywhere close to a consistent ratio of calcium to alk consumption and for you to push it is both ignorant and detrimental.

So what process besides the nitrogen cycle (which also returns Alk used) causes unbalanced Alk consumption?
 
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Yeah....like a dozen threads a week from somebody seeing their alk drop 2 dKH per day while their calcium stays the same.

Yep...they are hallucinating because they don't have a scientific basis.

Alk and calcium are not locked in a fixed ratio in captive tanks unless the calcifying organisms, aka large clams or rapidly growing SPS significantly outstrips the biological processes consuming alk, nitrate producing bacteria, etc. For many of not most reefers this is not the case. Some guy with a couple frags in his tank and a nitrate level of 30 isn't going to have anywhere close to a consistent ratio of calcium to alk consumption and for you to push it is both ignorant and detrimental.

Again. What biological process is consuming Alk and not calcium?
 
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@Randy Holmes-Farley

So it's time to lower my Ca.

1. Tank has been running for 9 months on balanced Ca/Alk. (Mostly Kalkwasser and some AFR)
2. In the last 138 days Ca went from 485 to 501 according to my last 2 ICP tests. An increase of roughly .12ppm per day.

I'm interested in bringing it back down without water changes. I'm thinking of switching from Kalkwasser dosing to baked baking soda for a short time.

By my calculations, I need to replace 7 dKH worth of balanced dosing with unbalanced dosing (7 dKH = 49ppm Ca).

I'm currently dosing 3240ml of Kalkwasser per day on my 400L tank. Roughly 0.9dKH per day.

Using baked baking soda, I would need "52.9 grams, approx 11.5 tsp, or 1.8 oz"

Here is my question:
Can/how could I dose this to get the same/similar pH benefits of Kalkwasser?

Is it as simple as mixing 5.9g of baked baking soda in 1440ml of RO/DI water and dosing at a rate of 1ml/min and repeating for 8 days?

Anything I should worry about? Will pH impact be higher or lower than Kalkwasser? Am I unbalancing something else by doing this?

Thanks in advance for the chemistry help.
 

Randy Holmes-Farley

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FWIW, the slow calcium rise is expected with limewater (kalkwasser). I used a low calcium mix (normal IO) for that reason.

If you want the same pH effect as the kalkwasser, you'll need to use sodium hydroxide.

If you just want the same alk effect, then you can use bicarbonate, carbonate, or hydroxide for the alk dosing.

The 7 dKH of alk is right.

You can dose that over any period you want.

If you spread it out over 14 days (0.5 dKH per day), then you'd dose about half as much limewater during that time.
 

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FWIW, the slow calcium rise is expected with limewater (kalkwasser).

Since I use kalkwasser exclusively to maintain Alk and Ca, I've noted this too over the years. Randy has mentioned that the corals incorporate other elements (such as strontium) that can take the place of calcium in their skeletons.

The method that I use to bring a calcium level down is simply to slightly reduce the amount of kalkwasser (which obviously will lower both) and then maintain the alkalinity at my preferred level with Seachem's Reef Builder for a while. Once the calcium level is back down to where I want it, I then go back to my previous kalkwasser concentration.

I only have to do this every 2 months or so since the rise in calcium is typically gradual.
 
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Since I use kalkwasser exclusively to maintain Alk and Ca, I've noted this too over the years. Randy has mentioned that the corals incorporate other elements (such as strontium) that can take the place of calcium in their skeletons.

The method that I use to bring a calcium level down is simply to slightly reduce the amount of kalkwasser (which obviously will lower both) and then maintain the alkalinity at my preferred level with Seachem's Reef Builder for a while. Once the calcium level is back down to where I want it, I then go back to my previous kalkwasser concentration.

I only have to do this every 2 months or so since the rise in calcium is typically gradual.

Thanks. That's exactly what I'm planning on doing. Just trying to select a product and figure out the dosing. Since I use Kalkwasser to maintain pH...would like to use something that helps maintain it.
 
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