GH+KH RO Reminiralzation Product Help.

[Wookii]

Right, so I tried dissolving them separately, each in 50ml of DI water:



No clouding at all and they both dissolve easily.

Then I mixed the two solutions together:



Instant clouding - so I assume this is some sort of precipitation?

The KNO3 is actually from my APFUK starter kit, so I’ll try the KNO3 I got from APC Pure to make double sure it isn’t an issue with the APFUK stuff.

 

[Wookii]

The KNO3 is actually from my APFUK starter kit, so I’ll try the KNO3 I got from APC Pure to make double sure it isn’t an issue with the APFUK stuff.

And the result . . . *drum roll* . . .



. . . no clouding at all!!!

So the Potassium Nitrate from APFUK is not actually Potassium Nitrate? Perhaps they supplied Calcium Nitrate instead?

EDIT: Actually it can’t be Calcium Nitrate as that would presumably give a higher Gh?

 

[dw1305]

Hi all,

My remaining issue is the CaCl2 + KNO3 solution. As you can see from the image the solution remains cloudy,

Something is wrong, three of the four constituents K+, NO3-, Cl- only form soluble salts, which means that whatever calcium (Ca++) compound is formed <"should be soluble">. Are you sure the bags aren't mixed up, if you had Ca++ and PO4--- together they would precipitate out as insoluble calcium phosphate (Ca3(PO4)2).

Edit: I see you've solved your problem.

Perhaps they supplied Calcium Nitrate instead?

Still the same issue you have nitrate, potassium and chloride ions, so there isn't an insoluble compound they could form with the calcium. "Insoluble" calcium salts we are likely to encounter are calcium sulphate (very slightly soluble), calcium carbonate (soluble in weak acids) and calcium phosphate (insoluble).

cheers Darrel

 

[Wookii]

Hi all,

Something is wrong, three of the four constituents K+, NO3-, Cl- only form soluble salts, which means that whatever calcium (Ca++) compound is formed <"should be soluble">. Are you sure the bags aren't mixed up, if you had Ca++ and PO4--- together they would precipitate out as insoluble calcium phosphate (Ca3(PO4)2).

Edit: I see you've solved your problem.

Still the same issue you have nitrate, potassium and chloride ions, so there isn't an insoluble compound they could form with the calcium. "Insoluble" calcium salts we are likely to encounter are calcium sulphate (very slightly soluble), calcium carbonate (soluble in weak acids) and calcium phosphate (insoluble).

cheers Darrel

I did wonder if I’d mixed up the KNO3 with the PO4 to start with but the two salts are visually very distinct, and the APFUK PO4 looks identical to the PO4 I have from APC Pure - a very fine white glistening crystalline salt vs the dull almost damp looking consistency of the APFUK KNO3.

The one difference between the APFUK KNO3 and the APC Pure KNO3 is the former was very ‘off-white’ in colour and the latter almost pure white in colour - though I can’t be sure the off-white is the result of aging/absorbing atmospheric moisture?

I’ve thrown most of the APFUK KNO3 away, but just tested the small lump I have left, and it definitely contains Nitrate:



Disclaimer before I get ostracised from the forum: I don’t use the Nitrate test routinely, just in this case to show a non-zero value with some of the APFUK KNO3 in some DI water.

 

[dw1305]

Hi all,

I’ve thrown most of the APFUK KNO3 away, but just tested the small lump I have left, and it definitely contains Nitrate:

View attachment 155847

Disclaimer before I get ostracised from the forum: I don’t use the Nitrate test routinely, just in this case to show a non-zero value with some of the APFUK KNO3 in some DI water.

No you are good. This is one situation where you can be pretty sure that the test kit will give you an accurate result, because you don't have any interfering ions or nitrite (NO2-) and you've started with DI water. The only possibility for error would be failing to mix the two reagents fully.

cheers Darrel

 

[Zeus.]

Which CaCL2 salt (hydrate) have you got there M8 ? pic of label/package may be helpful/insightful

 

[Wookii]

Which CaCL2 salt (hydrate) have you got there M8 ? pic of label/package may be helpful/insightful

It’s this one mate from APC Pure:

https://apcpure.com/product/calcium_chloride_77_5

Edit: It’s definitely not the Hexahydrate as that’s 20x the price, so I assume it’s the Dihydrate.

 

[Zeus.]

Which is CaCL2.2H2O- Calcium Chloride dihydrate which has a solubility of 134.5g/100ml
They can call it pure IMO as with it being a hydrate the 'impurity' is just H20

 

[Wookii]

So, I've now fully made the transition to RO water. Again, I fully appreciate that test kits are frowned upon in general terms, and I wouldn't normally use them beyond ensuring water is ammonia and nitrite free at tank start-up. However I had been using the GH and KH drip tests to ensure that my remineralised RO water is producing similar values to those I've targeted with the calculated dosing of the CaCl2, MGSO4 and K2CO3 (I had no other way to confirm the calculations worked in practice).

The RO water consistently comes out with a GH of 5.5-6 and KH or 2.5-3, which is exactly what I was aiming for with all the calculations in this thread. This is testing 25 litres of RO water which is fully dosed with remineralisation salts and daily dose of macro fert salts (KNO3, KH2PO4 and K2SO4). This RO water comes out with a TDS almost bang on 200ppm.

The anomalie that I'm encountering is when I test the actual tank water, the drip tests result in a GH of around 9-10, and a KH of around 5-6. I've done enough water changes (25% daily) now that the tap water the tank started off with should have been fully exchanged, and I have also done a number of pure RO water changes to bring the GH, KH and TDS down a little faster.

My first thought was that the fairly large amount of Sieryu stone I have in the tank, and the fact that the pH dips down to 6.1 during the CO2 period, might mean the stone is buffering the KH and GH? However when I tested the TDS on the tank last night, it came out at about 195ppm, lower than the remineralised RO water presumably due to the few changes of pure RO that I've done.

I'm happy to take it on the chin from people telling me "Test kits . . told you so . . ." but as I don't really do taking things on pure faith very well, what I'd really like to understand is what might be causing the anomalie in the drip tests. These tests seem capable on reliably confirming the approximate KH and GH of my RO water, and also confirm exactly the GH of my tap water shown on my water report. So are there some chemicals at play in the tank water that throw these tests so far out?

 

[dw1305]

Hi all,

My first thought was that the fairly large amount of Sieryu stone I have in the tank, and the fact that the pH dips down to 6.1 during the CO2 period, might mean the stone is buffering the KH and GH?

Would be my guess.

The anomalie that I'm encountering is when I test the actual tank water, the drip tests result in a GH of around 9-10, and a KH of around 5-6.....However when I tested the TDS on the tank last night, it came out at about 195ppm

The TDS (conductivity) reading should be right. It is a linear scale and pretty straightforward. That is why I like conductivity as a metric, it might not be that useful, but it will be accurate.

After that It is going to depend upon what the test kits actually measure. The dKH drop test <"measures alkalinity"> via an <"acid base titration">, and I have no personal experience of their accuracy.

I've no idea how the dGH kit works, but if it produces a white precipitate? It may use soluble dilute sodium hydroxide (NaOH) to <"form insoluble Ca(OH)2 and Mg(OH)2">.

You would also potentially get aluminium and iron hydroxides formed as well, although they wouldn't necessarily be white, and as the solution became <"more alkaline the aluminium ions would go back into solution">.

.....with the calculated dosing of the CaCl2, MGSO4 and K2CO3. (I had no other way to confirm the calculations worked in practice).

This is one situation where you can be pretty sure that the test kit will give you an accurate result, because ..........you've started with DI water.

But you actually know exactly how much dKH and dGH you have in your RO water, because it is the amount you've added, it is your standard. If the test kit numbers you've got are different? It is the test kit that is wrong.

The workings are in <"What do the three....">, derived from Larry Frank's very useful <"the Krib"> article.

cheers Darrel

 

[Wookii]

Hi all,

Would be my guess.

Thanks as always Darrel. Would the stone really release carbonates and calcium and magnesium that fast then to sustain such a large increase (doubling) of the GH and KH - bearing in mind the 25%+ daily water changes? Everything I've read seems to suggest the release is quite slow even with weekly water changes?

The TDS (conductivity) reading should be right. It is a linear scale and pretty straightforward. That is why I like conductivity as a metric, it might not be that useful, but it will be accurate.

That was my thinking too, which is why I can't reconcile the idea that the TDS can measure the same, but the GH and KH can be double. I appreciate the fert salts will be less diluted in the tank water, and some will also be used up, but is that likely to be enough to account for the same TDS but double the Ca/Mg and Carbonates? My only conclusion then is failure of the test solutions, or rather not their failure, but possibly something else throwing them out.

I've no idea how the dGH kit works, but if it produces a white precipitate? It may use soluble dilute sodium hydroxide (NaOH) to <"form insoluble Ca(OH)2 and Mg(OH)2">.

No, there is no precipitate, its a simple colour change (titration?) drop test kit also - one drop = 1dGH (or 0.5dGH if you double the test volume etc), keeping adding drops until the colour changes.

But you actually know exactly how much dKH and dGH you have in your RO water, because it is the amount you've added, it is your standard. If the test kit numbers you've got are different? It is the test kit that is wrong.

Sorry what do you mean here? Are you saying if the test kit measures the RO water correctly, then the measurements of the tank water are also correct? if so, how do we account for the TDS being the same?

 

[dw1305]

Hi all,

Sorry what do you mean here? Are you saying if the test kit measures the RO water correctly, then the measurements of the tank water are also correct?

No, I mean you don't need to measure the RO + salts water to get a dGH, or dKH, value. You know how much of each of the salts you've added, and from there you can <"work out exactly"> what the true dGH and dKH values are.

This is for dGH

By definition, 1dGH = 10 mg/liter CaO
Atomic Weight Ca = 40, O = 16, CaO = 56
So 10 mg/liter CaO contains 40/56 *10 = 7.143 mg/liter of Ca​

Atomic weight CaCO3 = 100
So 7.143 mg/liter of elemental Ca would be expressed as 100/40 * 7.143 = 17.8575 mg/liter(ppm) CaCO3.
1dGH = 17.86 ppm CaCO3 and 7.143 ppm Ca2+.

and this is for dKH

1dKH = 17.86 ppm CaCO3
From above; 1dKH = 17.8575 mg/liter CaCO3. 7.143 mg/liter of this is Ca, the rest ;(17.8575-7.143)= 10.7145mg/liter CO3
1dKH = 10.7145 ppm CO3

For magnesium (Mg) you still have convert it to its equivalent weight in CaO, but from <"James' Planted Tank">

1 dGH = 7.2mg/l Ca++
1 dGH = 4.3mg/l Mg++
............
1.8g KHCO3 in 25 litres of water = 2 dKH
1.2g K2CO3 in 25 litres of water = 2 dKH

how do we account for the TDS being the same?

The TDS value is almost certain to be accurate. It maybe that K+, PO4---, Mg++ and NO3- etc ions have been taken up by the plants and the additional TDS is from Ca++ and 2HCO3- ions that have gone into solution from the stone, but I'm dubious.

cheers Darrel

 

[Wookii]

Hi all,

No, I mean you don't need to measure the RO + salts water to get a dGH, or dKH, value. You know how much of each of the salts you've added, and from there you can <"work out exactly"> what the true dGH and dKH values are.

Ah, I see what you mean, thanks Darrel. yes, sorry, the testing of the remineralised RO is as more of a system test as much anything else - remember I'm dosing from pre-mix solutions via an auto-doser, rather than dry salts straight into the RO water, so a few places where things can go wrong (me messing up the mixes, dosing the incorrect proportions, doser drifting on calibration etc)..

The TDS value is almost certain to be accurate. It maybe that K+, PO4---, Mg++ and NO3- etc ions have been taken up by the plants and the additional TDS is from Ca++ and 2HCO3- ions that have gone into solution from the stone, but I'm dubious.

cheers Darrel

I'm dubious too. For simplicity, lets just consider the dGH, and assume the rocks are just giving up calcium carbonate, so if I've understood your conversions correctly, a 5dGH increase would be 17.86mg CaCO3 x 5 = 89.3mg per litre. Would be 89.3ppm contribution to TDS alone?

So in my 96 litre tank, that would would be 8.57 grams (89.3mg x 96l) of CaCO3 being released every few days? That seems a lot.

 

[dw1305]

Hi all,

Would be 89.3ppm contribution to TDS alone?

Unfortunately the "ppm" value for TDS and the ppm for from the salt addition aren't the same unit, mainly because different ions conduct different amounts of charge. The 100 microS ~ 64ppm TDS is where the predominant salts are Ca++ and HCO3-. If your main salt is NaCl (Na+ Cl-) then the conversion is 100 microS ~ 50ppm TDS.

remember I'm dosing from pre-mix solutions via an auto-doser, rather than dry salts straight into the RO water, so a few places where things can go wrong (me messing up the mixes, dosing the incorrect proportions, doser drifting on calibration etc)..

I'd forgotten that, and that makes sense.

So in my 96 litre tank, that would would be 8.57 grams (89.3mg x 96l) of CaCO3 being released every few days? That seems a lot

My thought as well, you pretty soon wouldn't have any rock left.

cheers Darrel

 

[Zeus.]

CaCl2, MGSO4 and K2CO3 .

This is testing 25 litres of RO water which is fully dosed with remineralisation salts

How much of each are you adding per 25l ?

 

[Wookii]

How much of each are you adding per 25l ?

Each respective 2.5 litre container has 288g CaCL2, 375g MgSO4 and 225g of K2CO3.

Each 25 litre RO water change gets a 20ml dose of each, so 2.3g CaCl2, 3.0g MgSO4 and 1.8g K2CO3.

 

[Zeus.]

 

[Wookii]

View attachment 156385
View attachment 156386

Thanks mate, that confirms all the previous calc's pretty much exactly, and also what I measure the re-mineralised RO water at using the drip tests.

Now I'd just like to figure out what's going on in tank.

I'm going to give it another week or two of just carrying on with the daily water changes as-is at the pre-determined dosing levels and then check again to see if the GH and KH has stabilised.

At that point if it hasn't I'm unsure of the way forward to determine if the test kits are at fault, or if indeed increases in GH and KH are happening in tank. I really need to be sure before I take any measures against reducing the reminseralisation salts added to the RO mix, for fear of making the water too soft.

 

[Zeus.]

that confirms all the previous calc's pretty much exactly,

Good, it also does another level on 'checking' on our calculations as well

 

[Wookii]

Good, it also does another level on 'checking' on our calculations as well

Do you know when the calculator will be released yet - will be good to have a play with it?

Incidentally I didn't realise quote how much K was being added by the K2CO3 (!) - we may need to revisit the K2SO4 dosing included on the calculator you sent my via PM?