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DIY Remineralisation Problems with Calcium Carbonate for KH


jalbright
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I'm finally getting around to trying DIY Remineralisation and I'm having issues with using calcium carbonate.  I'm wondering if anyone has experience with this?  I've read through a lot of the remineralization posts and it seems like most folks aren't trying to add KH, so there isn't much talk about it.

 

The calcium carbonate just doesn't seem to dissolve.  The water stays cloudy, my TDS is low, PH is high, and I get really strange behavior with the API GH/KH liquid tests.

I'm currently using Salty Shrimp GH/KH+ and RO water.  I mix about 4g into 5 gallons of water and get about 160 TDS, GH8, KH4, PH 7.8.  It dissolves and tests accurately almost immediately as I have a pump circulating in the bucket.

For the DIY test batch, I mixed 41g calcium sulfate hemihydrate, 20g calcium carbonate, and 39g magnesium sulfate into 800ml of ro water.  I dosed my 5 gallon bucket with about 32ml to give me roughly 4g (I figured this would be a good starting point as it's what I've been dosing the SS at).

I'm getting GH8 & KH3, but that's where the consistency ends.  My TDS reads at 106, PH is at 9.4, and the water is still cloudy after circulating for over an hour.  The GH and KH tests behaved strangely as well.  They initially read low, but changed back to orange and blue after sitting for a few minutes (as though slowly reacting to undissolved cal carb?), then I added additional drops and rechecked until they stayed green and yellow giving me the 8 & 3 reading.  I repeated this several times and the results were consistent each time. 

I didn't expect it to behave exactly like the SS as I gather they use different ingredients (calcium chloride, etc.), but these results seem all over the place.  I'm 99% certain that the issue is the calcium carbonate as I attempted to mix and test it separately at first and had a similar experience of it not dissolving and having oddly low TDS for the amount and KH reading.  After this I decided to mix the whole recipe and see how it went as I would have the SS to compare to. 

Any ideas?  I would love to hear from anyone who is making a DIY GH/KH mix.

 

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2 hours ago, jalbright said:

calcium carbonate

 

2 hours ago, jalbright said:

I'm 99% certain that the issue is the calcium carbonate as I attempted to mix and test it separately at first and had a similar experience of it not dissolving and having oddly low TDS for the amount and KH reading

Have you got a link of where you bought the Calcium carbonate? 

I bought mine from a brewing shop 

https://www.keg-king.com.au/calcium-carbonate-caco3-300g.html.html

 

And it has no problems dissolving in water. Afterall, they use it to make beer. 

It was bought already in powdered form, so it didn't take much to dissolve in water.

Edited by jayc
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I realized that I had some other cal carb on hand, so I was able to test with a second source as well.  One is sold for brewing and one as a supplement.

 

https://www.amazon.com/gp/product/B0064GZPPO/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

https://www.amazon.com/gp/product/B07B8V38GD/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

I just retested both of these and I'm still finding it difficult to dissolve.  TDS raises slowly and GH/KH tests act as above.  The cloudiness is less in the bucket I mixed 24 hours ago, but beyond that I'm concerned about not being able to use TDS as a quick check of my measured dosing.  Some days I'm mixing 4-5 5 gallon buckets and I don't have time to let them sit for hours to dissolve 😕

The TDS is really confusing me as well.  I mixed .5g into 50ml water, drew out 4ml in a syringe, and dissolved that into a pint of water.  This should give me .32g/gallon, which should give me a TDS of about 84ppm (1g/10 gallons = 26.5ppm per https://www.thekrib.com/Plants/Fertilizer/dosing.html).  This is further supported by the KH measurement of just under 5 (4 drops changed color, but not to a clear yellow, the 5th drop went clear yellow) @ 17.9ppm/1dKH

Yet, my TDS only raised about 10ppm in 10 minutes and to about 20ppm after 30 minutes(measured with two different pens).  I feel like I really must be missing something here, but I'm not sure what.

Edited by jalbright
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FWIW I'm reading that it is known to be relatively insoluble (unless you're injecting co2).  I wonder what the carbonates are derived from in the salty shrimp formula?

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14 hours ago, jalbright said:

 

Yet, my TDS only raised about 10ppm in 10 minutes and to about 20ppm after 30 minutes(measured with two different pens).  I feel like I really must be missing something here, but I'm not sure what.

i had this problem too, what i do is under mix,  i let my pre mixed water get to 100-110 initially then fast drip it in to my tank, after a few hrs i get the 140ish reading that i aim for. sir Jayc was the one who told me to under mix when i found my tds gradually rose as time passed and it worked fine for me.

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@jalbright, you might need to use less Calcium carbonate for your mix. And try using cold (from the fridge) water to dissolve it. 

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8 hours ago, superasitis said:

i had this problem too, what i do is under mix,  i let my pre mixed water get to 100-110 initially then fast drip it in to my tank, after a few hrs i get the 140ish reading that i aim for. sir Jayc was the one who told me to under mix when i found my tds gradually rose as time passed and it worked fine for me.

I'm not sure my precise nature can handle that, lol.  I've also got three people in my house with tanks (me, my wife, and my daughter) and they aren't all getting the same mix.  I have a big RO system with a big pressurized reservoir and we mix our buckets as we use them.  The TDS pen is our double-check to make sure the water is right for the tank it's going into.  It actually took  24-48 hours for the calcium carbonate to fully dissolve, but even an hour or two really doesn't work for our water change routine.

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4 hours ago, jayc said:

@jalbright, you might need to use less Calcium carbonate for your mix. And try using cold (from the fridge) water to dissolve it. 

Looks like more if anything.  Now that my mix has completely dissolved, I'm getting 120 TDS, GH8, KH 2, and PH 8.6

 

Looking at SS mixed to the same TDS (120), I get GH6, KH3, PH 7.8

One more thing to be confused about, why is the PH so much higher when the KH is lower?  If you can't tell, the inconsistency and unpredictability bothers me more than a little bit.  I'm feeling like this is going to be a failed experiment for me.

I've been trying to research alternative carbonate sources.  I was thinking about trying a mix of sodium bicarbonate and potassium carbonate.  They are both quite soluble in water and using both could mitigate adding too much sodium or potassium.  I mix my own dry ferts so I could can adjust the potassium down there as well if needed.  Thoughts?

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46 minutes ago, jalbright said:

why is the PH so much higher when the KH is lower?

Probably because you overdosed Calcium sulphate (by 3g) and magnesium (by 2g) lol Though, I'm having similar experiences when it comes to API GH/KH/PH test result reverting in color.

For my mix I add Calcium Sulphate Dihydrate (38g) + Calcium Carbonate (20g) + Magnesium Sulphate (37g) into 1L of 14ppm tap water. Then, I mix 35mL of this solution with 5 gallon of tap water, and I get water parameter of Ph:7.5, GH:7, KH:2.5 (at 2 drops, it's basically green..neither blue or yellow, therefore +0.5 lol), TDS: ~100ppm. Note, I didn't add any potassium (probably should), iron, or manganese, Seachem Prime that's why my TDS is so low. It's probably more important to have the right GH and KH rather than TDS..

My 1L mix also has a bunch of undissolved powder at the bottom but I give it a good stir before extracting it with a syringe. It clouds the tank for a good 1-2hrs (even if I drip my water back in). For my next batch I'll probably more Calcium Sulphate with Calcium Carbonate, maybe 5g, just to raise the KH a little more.

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27 minutes ago, xKen said:

Probably because you overdosed Calcium sulphate (by 3g) and magnesium (by 2g) lol

My understanding is that calcium and magnesium do not affect PH.

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3 hours ago, jalbright said:

I was thinking about trying a mix of sodium bicarbonate and potassium carbonate. 

I was just about to also suggest replacing your carbonate source from Calcium carbonate to Potassium carbonate.

Avoid Sodium Bicarb, in this case, if possible.

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1 minute ago, beanbag said:

what about potassium BIcarbonate?

It's considerably less soluble than potassium carbonate, from what I've read.

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21 hours ago, jayc said:

Avoid Sodium Bicarb, in this case, if possible.

Do you have any specific info regarding the amount of sodium that would be harmful to plants and inhabitants?  The amount of sodium added if I were to only use sodium bicarbonate looks to be in the 20-25ppm range for the KH I'm looking for and that's well within the level of many many municipal water sources. Also many hobbyists seem to use it without issue.

 

If I source my carbonates equally between the sodium bicarb and potassium carb it would be half that, which doesn't seem like enough to be concerned about.

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21 minutes ago, jalbright said:

20-25ppm range for the KH I'm looking for and that's well within the level of many many municipal water sources.

Yes but that will throw your TDS measurements out for a mineral that is not needed in a freshwater aquarium. Whereas, potassium is much more useful in an aquarium.

However, if you are mixing sodium and potassium carbonates, it's not too bad I suppose. It's just not how I would do it. But that doesn't mean that my way is the only way.

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31 minutes ago, jayc said:

Yes but that will throw your TDS measurements out for a mineral that is not needed in a freshwater aquarium. Whereas, potassium is much more useful in an aquarium.

No different than all of the sulfates then, right?  Agreed about the K, but I don't want to overdose that either.  It looks like the sodium bicarb will give about 8ppm sodium/ 1dKH and the potassium carbonate about 11ppm K / 1dKH.  That seems reasonable to me aiming for 3-4 dKH in the tanks we keep. 

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