Balancing Alkalinity after prolonged Kalkwasser usage

[Dennis Cartier]

After the recent discussion about pH and kalk usage (in the ACI thread), I started wondering about the best approach for dealing with the tendency of long term kalk to boost Calcium. My initial reaction would be to simply add a tiny 'make up' dose of alk to offset the kalk, but all the typical alkalinity additives would raise sodium if not combined with an adjustment of chloride.

I guess the first step in coming up with an approach is to quantify how much alkalinity is deficient in each liter of saturated kalkwasser?

Dennis

 

[Dennis Cartier]

I am doing my own research to answer the question, but I suspect the answer is going to be it depends. In other words, I expect there is no concrete answer.

So lets change it up a bit. If I wanted to use KOH as a potassium supplement, instead of the typical potassium chloride, that would give me a slight alk bump in addition to the potassium. I am having trouble figuring out how much potassium is in each g of KOH though. For that matter how much alkalinity is in each g as well?

Dennis

 

[Randy Holmes-Farley]

As I often say, there's no perfect method to supplement calcium and alkalinity. All have pros and cons of various sorts.

The imbalance with calcium to alk is one of the cons of kalkwasser.

I resolved it by just using a high alk/lower calcium mix (normal IO) and calcium balanced out at 472 ppm long term using 1% daily water changes.

The boost to sodium from an occasional correction is, of course, not nearly as large as using just sodium carbonate and calcium chloride for alk and calcium.

let's look...

Suppose you add 2 dKH of alk every day using kalkwasser. That means adding 14.3 ppm of calcium each day. A pretty high demand scenario.

Take an extreme case where you have the most magnesium-consuming organism we typically keep: coralline algae.

Aquarium Chemistry: Magnesium In Reef Aquaria

This article details the nature of magnesium in seawater, how it is added, measured, and removed from marine aquaria, and how it impacts the maintenance of calcium and alkalinity.

reefs.com

Pure calcium carbonate is 40% calcium (and 60% carbonate) by weight.

Let's assume coralline is as reported in the literature for Corallina pilulifera to be 4.4% magnesium by weight in its calcium carbonate. That 4.4% magnesium displaces calcium to the extent of 7.2% of the weight of the calcium carbonate (because calcium weighs more than magnesium, more of the weight % of calcium is removed for the given weight percent of magnesium incorporated).

Thus, for each carbonate deposited, we are using less calcium. The magnitude is about 40-7.2/40 = 82% of what we would use for pure calcium carbonate.

In our original scenario (pure calcium carbonate) we assumed:

2 dKH per day
14.3 ppm of calcium each day

But in this coralline consumption, we are consuming about:

2 dKH per day
14.3 x 0.82 = 11.7 ppm calcium per day
1.6 ppm magnesium

Now we just need to calculate how much sodium carbonate (or bicarbonate or hydroxide, all give identical results) is needed to offset this difference between the calcium added and the calcium consumed.

Difference is 14.3 -11.7 ppm per day = 2.6 ppm per day

Using our consumption ratio of 2 dKH per 11.7 ppm of calcium, we now know tht we need to add extra alk to the tune of 2 dKH *(2.6 ppm/11.7 ppm) = 0.44 dKH per day.

How much is that and what does it do to sodium?

0.44 dKH is 0.16 meq/L or 0.16 mM sodium bicarbonate.

0.16 mM sodium bicarbonate contains 3.7 mg/L sodium (since sodium weighs 23 mg/mmole).

Thus, we are adding 3.7 ppm of sodium each day.

In the course of a month we are adding 115 ppm. The normal background of sodium is about 10,500 ppm, for a 1.1% rise in sodium.

If you maintain salinity, that rise gets corrected to a 0.33% rise in sodium and a 0.66% drop in everything else (since sodium is about 1/3 of the mass of ions in seawater).

Is this significant in a month or a year?

Month? Definitely no. A year? Maybe, but I doubt it.

For comparison to the variability in sodium caused by different salt mix and different processes in reef tanks that folks think are good, take a lot at a bunch of random ICP values for sodium.

I'll do it now, but your results will vary.

Here's what I find for the most recent 10 ICP values I find by searching this forum:

10,468 ppm
10,495
13,486 (high salinity issue)
11,654
11,027........10,945......(two ICP companies, same tank)
9653
10,348
10,210
11,154
10,210
10,100


As we can see, there's lots of variability in sodium between tanks, and there no evidence that sodium a little high or low is a concern.

 

[townclown]

I'm trying to figure out your goal here. Correct me if I'm wrong, but you're looking to use Kalk as a calcium supplement?

 

[Randy Holmes-Farley]

I am doing my own research to answer the question, but I suspect the answer is going to be it depends. In other words, I expect there is no concrete answer.

So lets change it up a bit. If I wanted to use KOH as a potassium supplement, instead of the typical potassium chloride, that would give me a slight alk bump in addition to the potassium. I am having trouble figuring out how much potassium is in each g of KOH though. For that matter how much alkalinity is in each g as well?

Dennis

Using KOH is far more likely to result in an imbalance than is sodium hydroxide (or carbonate/bicarbonate) because there is 26x more sodium to begin with.

KOH is 70% potassium.

 

[Randy Holmes-Farley]

I'm trying to figure out your goal here. Correct me if I'm wrong, but you're looking to use Kalk as a calcium supplement?

The issue is that using calcium hydroxide as an alk and calcum supplement long term to maintain alk will slowly cause calcium to rise because not all the calcium is used to make calcium carbonate, since magnesium gets into the calcium carbonate in place of some of the calcium.

 

[townclown]

The issue is that using calcium hydroxide as an alk and calcum supplement long term to maintain alk will slowly cause calcium to rise because not all the calcium is used to make calcium carbonate, since magnesium gets into the calcium carbonate in place of some of the calcium.

Yea, I didn't think this was the route to take in order to maintain calcium. It also sounds complicated. May I ask for your tank specifications? @Dennis Cartier

 

[Dennis Cartier]

The issue is that using calcium hydroxide as an alk and calcum supplement long term to maintain alk will slowly cause calcium to rise because not all the calcium is used to make calcium carbonate, since magnesium gets into the calcium carbonate in place of some of the calcium.

I also have it a bit worse as I have elevated Magnesium as well. Last I checked about 1380. I think that may also contribute to skewing my Ca a bit higher. The reason for elevation in Mg for me is that I have a small tube of TLF ReMag on the final stage of my CaRx before it enters an aeration tower. I was getting precipitation depending on the pH I was aerating to and I was hoping that keeping the CaRx effluent Mg rich might help to moderate the precipitation.

It all might be moot in the end anyway. I have noticed that my pH decreases when I have my CaRx get auto shutdown based on the KH level. I was looking to see if the pH was unaffected when the CaRx was being paused as confirmation that my aeration tower was successfully stripping excess CO2. The decrease in pH is a bit unexpected and frankly confusing. I have no idea why that would happen. I have tweaked my CaRx control to alter the duty cycle of my peristaltic pump rather than shutting down completely to hold a target of 8.5 dKH.

I currently use the CaRx for 50% of my supplementation and kalk for the other 50%. In the last 24 hours, my KH averaged 8.535 dKH with a spread of 0.11 dKH (tested every 6 hours) and my pH averaged 8.375 with a spread of 0.1 pH (tested at same time as KH). So I am fairly pleased with my stability for KH and pH.

Thanks for the info Randy.

Dennis

 

[Randy Holmes-Farley]

I currently use the CaRx for 50% of my supplementation and kalk for the other 50%. In the last 24 hours, my KH averaged 8.535 dKH with a spread of 0.11 dKH (tested every 6 hours) and my pH averaged 8.375 with a spread of 0.1 pH (tested at same time as KH). So I am fairly pleased with my stability for KH and pH.

I'd be pleased. That sounds very stable.

 

[arking_mark]

So here is what I found with my tank...

1. Tank had been running for 9 months on balanced Ca/Alk. (Mostly Kalkwasser and some AFR)
2. After my last 2 ICP tests (138 days apart) Ca went from 485 to 501. An increase of roughly .12ppm per day.
3. By my calculations, I needed to replace 7 dKH worth of balanced dosing with unbalanced dosing (7 dKH = 49ppm Ca) to get back down to 450ish.
4. My tank consumes ~1dKH per day. I ended up using TM Classic Balling Alk to do my adjustments. I lowered my kalk dosing by 0.3dKH, left my AFR dosing alone (0.3dKH), and dosed 0.3ish TM Balling Alk.
5. After about 24 days, my non-ICP testing confirmed the expected relative drop of about 50ppm.

The benefits of this approach were that it had little impact on my pH which I still tightly control. I'm guessing my CO2 scrubber was working a little harder.

 

[J1a]

I suppose we can always use magnesium formate to "balance" the Ca/Mg/kH.

 

[Randy Holmes-Farley]

I suppose we can always use magnesium formate to "balance" the Ca/Mg/kH.

True, or even possibly magnesium hydroxide added as a slurry.

 

[Dennis Cartier]

True, or even possibly magnesium hydroxide added as a slurry.

Someone recently said that magnesium hydroxide "is essentially insoluble in water". I was surprised by that claim, but you would know, is it soluble?

 

[Randy Holmes-Farley]

Someone recently said that magnesium hydroxide "is essentially insoluble in water". I was surprised by that claim, but you would know, is it soluble?

Insolubility is in the eye of the beholder. It's a matter of the actual solubility and what amount is useful or significant.

It is poorly soluble in RO/DI. Wikipedia says 0.00064 g/100 mL at 25 °C. It is much less soluble in kalkwasser (due to all the hydroxide already there).

But it will dissolve in seawater because it it not yet saturated in seawater.

The small bluish white cloud on dosing a high pH additive is likely transiently precipitation magnesium hydroxide that will redissolve as it mixes into lower pH tank water.

That's why I suggested one might need to use a slurry.

You could also dissolve it in vinegar and dose that way.

 

[Dennis Cartier]

Just to confirm my math. If I am making a solution of KOH at 0.1N, KOH has a weight of 56g/mol, so I would use 5.6g/L and that would give me a solution with 3,897.6 mg/L of K. If I dose 3 ml/day into 300L, that should raise K by 1.17ppm over a month.

The 1L of solution will last me 333 days, so the 1 pound of KOH I ordered earlier will last me ... 74 years ... Hmmm, I had better eat more vegetables.

 

[Randy Holmes-Farley]

Just to confirm my math. If I am making a solution of KOH at 0.1N, KOH has a weight of 56g/mol, so I would use 5.6g/L and that would give me a solution with 3,897.6 mg/L of K. If I dose 3 ml/day into 300L, that should raise K by 1.17ppm over a month.

The 1L of solution will last me 333 days, so the 1 pound of KOH I ordered earlier will last me ... 74 years ... Hmmm, I had better eat more vegetables.

What is its purpose?

You are only adding 0.0028 dKH (0.001 meq/L) each day.

0.1 M is 100 meq/L. Dilute 3 mL into 300 L and it is diluted 300,000 times, to only 0.001 meq/L.

 

[Dennis Cartier]

The intent is to supplement potassium. I know the amounts are a bit like draining the ocean with a spoon

This is just the starting point. I will work my way up to find a level that keeps potassium at the proper level.

I am going to take it as a yes. I did not hear anything that sounded like a flaw in my calculations, just the premise!

 

[Randy Holmes-Farley]

The intent is to supplement potassium. I know the amounts are a bit like draining the ocean with a spoon

This is just the starting point. I will work my way up to find a level that keeps potassium at the proper level.

I am going to take it as a yes. I did not hear anything that sounded like a flaw in my calculations, just the premise!

The potassium calculations are OK.

That's a pretty slow addition. lol

 

[Dennis Cartier]

Lol, that is because I have to replace my Salifert test. It is my least favourite test to run. The nasty white waxy buildup that you need to clean out of the vial specifically. I wish there was a way to dissolve it rather than having to scrub it out.

 

[LBakker]

Just to confirm my math. If I am making a solution of KOH at 0.1N, KOH has a weight of 56g/mol, so I would use 5.6g/L and that would give me a solution with 3,897.6 mg/L of K. If I dose 3 ml/day into 300L, that should raise K by 1.17ppm over a month.

The 1L of solution will last me 333 days, so the 1 pound of KOH I ordered earlier will last me ... 74 years ... Hmmm, I had better eat more vegetables.

How will this effect the ph of the system as a KOH will boost the ph level?