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Reaction/precipitation of dry salts (fertilization + remineralization)

arcturus

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Hi!

I am using the following salts for macro fertilization:
  • Calcium Nitrate Tetrahydrate Ca(NO3)2*4H2O -> 20ppm NO3
  • Monopotassium Phosphate KH2PO4 -> 3ppm PO4 + 1.3ppm K
I am using RO water for water changes. The remineralization salts are the following:
  • Magnesium Sulphate MgSO4*7H20 -> dGH ~2° as Mg
  • Calcium Chloride CaCl2*2H2O -> dGH ~3.5° as Ca
  • Potassium Bicarbonate KHCO3 -> dKH ~1.5° + 20ppm K
Note: I am using Calcium Nitrate instead of Potassium Nitrate as a NO3 source to reduce the total amount of Potassium. The Potassium Bicarbonate used for remineralization already adds ~20ppm K. This means that Potassium will be dosed once a week along with the water change and the rest of the macros will be dosed during the week. This is for a tank with CO2 injection.

Questions:
  • Can I dissolve the two macro salts together (Calcium nitrate + Monopotassium phosphate) in the same container (to be used with a dosing pump)? Or will they react if mixed?
  • Can I dissolve the three remineralization salts together (Magnesium Sulphate + Calcium Chloride + Potassium Bicarbonate) in the RO water tank? The RO water tank (~90 litre) has a small circulation pump and I will let RO water rest for ~24h before adding it to the aquarium. Will these salts react if mixed together? Is it preferable to dissolve these salts separately and add them directly to the tank (and not to the RO water tank)?
Thanks!
 

Hufsa

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I remember Calcium nitrate being a naughty one, maybe this thread has the answer for your situation, I would look at this and this post especially.
Basically any time @X3NiTH posts you should get your online bookmark ready cause its always very informative :lol:
If these threads are not applicable for your situation (I must admit I glossed over a few bits) then I think he needs to respond himself
 

arcturus

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I remember Calcium nitrate being a naughty one, maybe this thread has the answer for your situation, I would look at this and this post especially.
Basically any time @X3NiTH posts you should get your online bookmark ready cause its always very informative :lol:
If these threads are not applicable for your situation (I must admit I glossed over a few bits) then I think he needs to respond himself
Thanks! I have read those threads. But then I read other users reporting using these salts in a "all in one" mix without issues. So, I am confused - and chemistry is not my background. I can revert to Potassium Nitrate instead of Calcium Nitrate as a source of NO3. But then I will end up with a weekly total of +40ppm K because of the Potassium Bicarbonate. This would mean that K will accumulate up to ~80ppm in the tank in the longer term. And then again, some say this level of K is irrelevant while other says is an extreme value that must be avoided.

The same applies to the remineralization salts. Several recipes mix these three salts together. But then some users say that those salts cannot be mixed due to precipitation - but if these salts precipitate when dissolved in ~90 litres of water, then they are simple not appropriate for the task. So, again, I am confused...
 

Ria95

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  • Can I dissolve the two macro salts together (Calcium nitrate + Monopotassium phosphate) in the same container (to be used with a dosing pump)? Or will they react if mixed?
Thanks!

It's possible to make a solution of both. Precipitation is also possible with higher concentrations in the solution. Try with small volume and see.

  • Can I dissolve the three remineralization salts together (Magnesium Sulphate + Calcium Chloride + Potassium Bicarbonate) in the RO water tank? The RO water tank (~90 litre) has a small circulation pump and I will let RO water rest for ~24h before adding it to the aquarium. Will these salts react if mixed together? Is it preferable to dissolve these salts separately and add them directly to the tank (and not to the RO water tank)?
If I understand you correctly you want to dissolve the 3 compounds in the entire volume of RO water to be replaced. That works, basically you will have the same concentrations you will have in your tank. It's the way to do it.

The salts should not be mixed together to make a concentrated master solution. Often these master solutions are 100x-1000x more concentrated than the levels you have in the aquarium.
 
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arcturus

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It's possible to make a solution of both. Precipitation is also possible with higher concentrations in the solution. Try with small volume and see.


If I understand you correctly you want to dissolve the 3 compounds in the entire volume of RO water to be replaced. That works, basically you will have the same concentrations you will have in your tank. It's the way to do it.
Exactly. I want to dissolve the three remin salts (Magnesium Sulphate + Calcium Chloride + Potassium Bicarbonate) in a tank with ~90 litres of RO water. I have a small circulation pump inside the RO water tank. The idea is to fill the separate RO water tank with RO water, add the three salts, let the water rest for ~24h with the circulation pump on (to aerate, warm the water a bit, and dissolve the salts), and then add these ~90 litres of water to the tank during the water change. I assume they cannot precipitate (otherwise the salts are not appropriate, because, as you said, these salts will be in the same concentration as in the tank!), but then I read that the Sulphate and Chloride always react (but this should be only when highly concentrated, which is not the case).
 

Ria95

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Yes, that will work as you describe. All the salts above dissolve easily so just adding them in the current of the pump should be enough .
 

bazz

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I add 4g x Calcium Nitrate, 4.5g x Calcium Sulphate, 4.5g x Calcium Chloride, 9g x Magnesium Sulphate and 3g x Potassium Carbonate to 130l of water resulting in 4.79 dGH and 0.94 dKH, every week using a small circulation pump without any problems.
If for any reason my water change gets knocked back a day or two (because of the pub) the mixture will begin to turn cloudy but this disappears within a couple of hours once it enters the aquarium.
Cheers!
 

arcturus

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I add 4g x Calcium Nitrate, 4.5g x Calcium Sulphate, 4.5g x Calcium Chloride, 9g x Magnesium Sulphate and 3g x Potassium Carbonate to 130l of water resulting in 4.79 dGH and 0.94 dKH, every week using a small circulation pump without any problems.
If for any reason my water change gets knocked back a day or two (because of the pub) the mixture will begin to turn cloudy but this disappears within a couple of hours once it enters the aquarium.
Cheers!

Why are you using Calcium Nitrate in the remineralizer mix? Or is this part of your fertilizer mix? Are you dosing fertilizers at once with the weekly water change or in multiple days? BTW, do you use CO2?

Do any of you have any input or tips regarding the fertilizer solution? As said above, I would like to use Calcium Nitrate and Monopotassium Phosphate as NO3 and PO4 sources. These two salts would be dissolved together in a 500 or 1000ml container and used in a period of 3-4 weeks using an automatic dosing pump. Can I dissolve and mix these two salts in the same 500-1000 ml container? Or will they react?

Or should I use Potassium Nitrate instead of Calcium Nitrate as NO3 source? Will the Potassium Nitrate react with the Monopotassium Phosphate? The issue with this option is that the long term accumulation of potassium in the water will be ~80ppm because of the K coming from potassium nitrate in the fertilizer plus the potassium bicarbonate in the remineralizer. Isn't this K value too high?
 

X3NiTH

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I’m at work at the moment so don’t have time for a long explanation.

You can mix Calcium Nitrate and Potassium Phosphate but the mixture needs to be acidified to prevent precipitation, without the acid the Calcium will precipitate with the phosphate forming a very insoluble Calcium Phosphate, it will even react together as dry salts in a bag together as the Calcium Nitrate likes to absorb atmospheric water and when they react you get insoluble rocks as hard as teeth!

:)
 

arcturus

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I’m at work at the moment so don’t have time for a long explanation.

You can mix Calcium Nitrate and Potassium Phosphate but the mixture needs to be acidified to prevent precipitation, without the acid the Calcium will precipitate with the phosphate forming a very insoluble Calcium Phosphate, it will even react together as dry salts in a bag together as the Calcium Nitrate likes to absorb atmospheric water and when they react you get insoluble rocks as hard as teeth!

Thanks for the input! So, I see the following options:
  • Option 1
    • Use Potassium Nitrate + Potassium Phosphate as NO3 + PO4 macro fertilizers, mixed together in a ~500ml container and dosed during the week using a dosing pump.
    • Remineralize the RO water and dissolve the following in a ~90 litre RO water container:
      • Potassium Bicarbonate to raise KH to 1-2 dKH°
      • Calcium Chloride + Magnesium Sulphate to raise GH to ~6° dGH
    • This option would end up with +80ppm of Potassium in the water after a few weeks (this is considered an extreme value by some sources and an irrelevant value by others...)
  • Option 2
    • Same as above, but replacing Potassium Bicarbonate with Magnesium Carbonate to raise dKH and dGH (this would be dissolved in a 90 litre container, so it should be possible).
    • This option seems ideal because I can control the total level of Potassium, since the remineralizer would not add any Potassium.
  • Option 3
    • Use Calcium Nitrate for NO3 as a dry salt and dissolve it directly in the tank. This means I would be dosing NO3 all at once after the WC and not during the week.
    • Remineralize the RO water as in option 1.
    • With this approach I can keep the level Potassium at ~20ppm (less is not possible unless I do not use Potassium Bicarbonate to raise KH).
Mixing Calcium Nitrate and Potassium Phosphate will potentially cause issues you described, so I am ruling that option out.

I would have no problem skipping the daily macro fertilizing and using dry salts instead of solutions and dosing them once a week directly in the tank after the water change. However, several sources here and elsewhere say macros should be divided several times per week in a tank with CO2 injection using the EI regime.
 

X3NiTH

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I would go for Option 2 but I would blend some Magnesium Sulphate as well as the Magnesium Carbonate so there is some Sulphur in the tank, you only need to target a couple of ppm SO4 to have enough for plants.

No issues with front loading the ferts at waterchange as long as you keep up dosing micro. You can test for macro uptake during the week to see any uptake rate and dose the difference to ensure these don’t bottom out.

When and how you add the ferts doesn’t really matter as long as they are there day in day out.

:)
 

arcturus

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I would go for Option 2 but I would blend some Magnesium Sulphate as well as the Magnesium Carbonate so there is some Sulphur in the tank, you only need to target a couple of ppm SO4 to have enough for plants.

No issues with front loading the ferts at waterchange as long as you keep up dosing micro. You can test for macro uptake during the week to see any uptake rate and dose the difference to ensure these don’t bottom out.

When and how you add the ferts doesn’t really matter as long as they are there day in day out.

:)
Many thanks! Front loading the macros at water change would greatly simplify the process. I will add micros daily.

Regarding SO4 (and Cl), since I am using RO water and will remineralize it to ~6° dGH, I will end up with ~55ppm Cl and ~68ppm SO4.

A side question: would macro nutrient intake be any different if the same dose is spread over several days or on a single day? I assume plant intake does not increase depending on the concentration of nutrients in the water column (if nutrients are always above minimum limits). Or does it?
 

MichaelJ

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Many thanks! Front loading the macros at water change would greatly simplify the process. I will add micros daily.
Hi @arcturus For what it is worth, I have been front loading all NPK Ca Mg for the week with my weekly WC, for a long time now in both my Low-tech tanks. Specifically CaSO4, MgSO4, Mg(NO3)2, KH2PO4 and recently Mg Gluconate and K2CO3. I usually let my pure RO water sit for half a day or so, to let it reach pH equilibrium (aka letting the CO2 degas to avoid any CO2 fluctuations). After I add the water to my tanks I wait 12-24 hours before I add micros/traces (I dose traces twice per week + a mid week dose of Fe Gluconate, if I remember). I haven't experienced any issues - except for an occasional and very temporary cloudiness when I dose the Fe Gluconate - allegedly due to interaction with my relatively high PO4 levels - plants are very healthy.

Cheers,
Michael
 

MichaelJ

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You can mix Calcium Nitrate and Potassium Phosphate but the mixture needs to be acidified to prevent precipitation, without the acid the Calcium will precipitate with the phosphate forming a very insoluble Calcium Phosphate, it will even react together as dry salts in a bag together as the Calcium Nitrate likes to absorb atmospheric water and when they react you get insoluble rocks as hard as teeth!

:)
This is why I love UKAPS! ... I never did Ca(NO3) myself (only Mg(NO3)) in part because I never heard of anyone doing it... And now I know why!

Cheers,
Michael
 
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arcturus

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Hi @arcturus For what it is worth, I have been front loading all NPK Ca Mg for the week with my weekly WC, for a long time now in both my Low-tech tanks. Specifically CaSO4, MgSO4, Mg(NO3)2, KH2PO4 and recently Mg Gluconate and K2CO3. I usually let my pure RO water sit for half a day or so, to let it reach pH equilibrium (aka letting the CO2 degas to avoid any CO2 fluctuations). After I add the water to my tanks I wait 12-24 hours before I add micros/traces (I dose traces twice per week + a mid week dose of Fe Gluconate, if I remember). I haven't experienced any issues - except for an occasional and very temporary cloudiness when I dose the Fe Gluconate - allegedly due to interaction with my relatively high PO4 levels - plants are very healthy.

Cheers,
Michael
BTW, any reason you are using Mg(NO3)2 instead of KNO3 as NO3 source?
 

MichaelJ

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BTW, any reason you are using Mg(NO3)2 instead of KNO3 as NO3 source?
Hi @arcturus Yes, its kind of a long and winding tale, so here goes... I used to blend tap-water with my RO water to make up for the KH target and K target... our household water-softener is using Potassium Chloride (KCl) as the resin to remove Ca and Mg, so our tap water (all taps inside the house) comes out at "zero" GH but very, very high on Potassium (K) - likely in the 140-160 ppm range ... so I never needed to add any additional K before when I mixed in tap water, so instead of KNO3 I opted for Mg(NO3)... an additional benefit is that I can lower my use of MgSO4... (our tanks don't need all that Sulphate we get from the SO4...) Things have changed, now I am back to 100% RO with a pinch of K2CO3 to make up for the KH and K requirements, I still kept the Mg(NO3)2 as I still don't want to use more MgSO4 than necessary... In the grand scheme of things I am always in pursuit of chemicals that reduces the overall TDS footprint for the sake of my livestock (Osmotic pressure mainly... but also the pure unknowns). I recently cut my MgSO4 in half and replaced it with Mg Gluconate. I am still targeting ~10 ppm of Mg in total but its spread out over Mg(NO3)2, MgSO4 and Mg Gluconante. My WC water for my densely planted shrimp tank is essentially ~15 ppm of NO3, ~4 ppm of PO4, ~20 ppm of K, 30 ppm of Ca and 10 ppm of Mg + about 30 ppm of totally unnecessary Sulphate that I wish I could avoid (Yes, I know I need a few ppm's of S) :) My other tank is a bit different with respect to the NPK targets, but I am using the same compounds there. Both tanks are doing very well.

Cheers,
Michael
 
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bazz

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Why are you using Calcium Nitrate in the remineralizer mix? Or is this part of your fertilizer mix?
I have been using it in small amounts in conjunction with other salts for years, since there was a thread on here (I can't seem to find it) many years ago where a lot of people were claiming to have better growth when nitrate wasn't solely supplied via KNO3.
Or is this part of your fertilizer mix?
No, Fertz consist of KNO3, KH2PO4, MgSO4 and a dash of Urea.
Are you dosing fertilizers at once with the weekly water change or in multiple days?
Macro and Micro dosed on alternate days three times each/week.
BTW, do you use CO2?
Yes.
I would just like to point out that I have no stems apart from a small bunch of H Pinnatifida, just Crypts, Buce, 2 x Anubius and 1 x Narrow Leaf Java Fern.
Also keeping one eye on the levels of Potassium which can become excessive using KNO3, KH2PO4 for Fertz and K2CO3 for Remin, but that's another story.
Cheers!
 
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