RO system, worth the "hassle"?

[MichaelJ]

If there's very small alkalinity and you aim to inject, say, 20 mg/L CO2, you'll push pH too low.

Discussions about preferability of SO4 or Cl sometimes appear. I've failed to find an argument which would persuade me to prefer one to another. You think chlorides are worse than sulfates? Why?

Yes, we discussed this on a couple of occasions. As with a lot in this hobby the pros / cons depends on your particular aspirations... For me its mostly a livestock consideration. My main issue with CaCl2 vs. CaSO4 is that the resulting EC/TDS from the same amount of Calcium is higher when using CaCl2 vs. CaSO4 - as much as 50% higher EC according to my own and this experiment. Keep in mind that with either one, if you target say a relatively common 3-4 dGH (say if you're keeping shrimps) you get an abundance of either Cl or SO4. However, while both S and Cl are considered essential nutrients, S is a macro while Cl is a micro and usually only present in tiny amounts in natural (tropical) waterways. Another argument against CaCl2 is the impurities which includes such things as arsenic, alkali chlorides, fluorides and heavy metals. Common impurities in CaSO4 are relatively benign Si, Fe. If keeping TDS low (mainly for the sake of the livestock) is not a concern or your targeting very, very low levels of Ca then CaCl2 is just fine. Now, one argument in favor of CaCl2 is the way higher solubility over CaSO4, but that only comes into play if you need to (for your own convenience) pre-batch your remineralization into high concentration dosing bottles.

Cheers,
Michael

 

[Wookii]

For me its mostly a livestock consideration. My main issue with CaCl2 vs. CaSO4 is that the resulting EC/TDS from the same amount of Calcium is higher when using CaCl2 vs. CaSO4 - as much as 50% higher EC

Unless you have some evidence I've not seen yet Michael, I not convinced the difference in TDS really makes that much difference to livestock - though happy to accept that the Chloride is not found in high concentrations in tropical waters which isn't ideal.

What is the difference in your total tank TDS using CaSO4 over using CaCl2? I use the latter along with MgSO4 to maintain 4-5dGH, with a fair amount of ferts, not EI, but not @_Maq_ style lean either, and my tank still sits rock solid at 93ppm TDS. Even if moving to CaSO4 reduced that to 70-80ppm TDS, I'm not sure that is going to make much of any difference to the livestock?

Now, one argument in favor of CaCl2 is the way higher solubility over CaSO4, but that only comes into play if you need to (for your own convenience) pre-batch your remineralization into high concentration dosing bottles.

This is the big one for me - I auto-dose and at 2.4g/L solubility its a non-starter compared to CaCl2 with 1,345g/L solubility.

 

[MichaelJ]

What is the difference in your total tank TDS using CaSO4 over using CaCl2?

Hi @Wookii, This is a test I did sometime ago:

Targeting ~20 ppm of Ca in 1 US gallon (3.78L) of water:

Starting point in both tests are equal temperature pure RO-DI water with a TDS of ~2 ppm.

Test 1:
Added and dissolved 0.33 g of CaSO4.2H2O. : TDS 62 ppm (124 uS/cm).

Test 2:
Added 0.28g of CaCl2.2H2O: TDS 125 ppm (250 uS/cm).

For typical levels of Ca (in this case 20 ppm) the difference is quite significant. Roughly twice the TDS/EC - as you increase the concentration of CaSO4 or CaCl2 the difference narrows. And of course for very, very low levels of Ca (say 2ppm) it hardly matters to the livestock if the TDS from CaSO4 or CaCl2 contributes 5 ppm or 10 ppm.

I'm not sure that is going to make much of any difference to the livestock?

As shown above targeting 20ppm of Ca makes a 60 ppm difference in TDS that is a big difference in terms of osmotic pressure especially for soft water fish and invertebrates such as shrimps. Of course, that number needs to be considered relative to your overall TDS from all the other compounds etc. and "background TDS" from decomposing fish, plant and food waste. If your TDS is a respectable 150 ppm (300 us/cm) shaving off 60 ppm - while beneficial - might not matter a whole lot, but if its a high 300 ppm a 60 ppm decrease may just be what your critters will be very thankful for.

This is the big one for me - I auto-dose and at 2.4g/L solubility its a non-starter compared to CaCl2 with 1,345g/L solubility.

Right on! And I totally understand that compromise.

Personally, I am trying to keep my TDS as low as possible. Again, it's all for the sake of the livestock for me trying get as close as possible to natural conditions. I don't think my plants care about TDS (within reason) as long as they get the nutrients they need... which from experience over the last couple of years turns out to be very little of everything

Cheers,
Michael

 

[_Maq_]

If keeping TDS low (mainly for the sake of the livestock)

First, I'm not sure whether animals perceive conductivity the way our EC meters do. My lay guess is they perceive primarily osmotic pressure. Yet I'm unable of making even approximate calculations. Secondly, with all respect, I somewhat doubt what you say (and surely will test on the first occasion) that the same volume [molar] of CaCl2 will increase conductivity notably more than CaSO4. My (hazy, amateurish) perception of charge density leads to an opinion that it's roughly the same.
I may be completely mistaken, of course.

Another argument against CaCl2 is the impurities which includes such things as arsenic, alkali chlorides, fluorides and heavy metals. Common impurities in CaSO4 are relatively benign Si, Fe.

Wow. Do you know from serious source? Does it not depend on the original matter which the chemicals are made from? Yes, everything is manufactured in China, but is really all calcium chloride in the world made in the same way from the same resource (marine water, perhaps)?

However, while both S and Cl are considered essential nutrients, S is a macro while Cl is a micro and usually only present in tiny amounts in natural (tropical) waterways.

I disagree. I've read statistics on world's freshwater sources and molar content of sulfur and chlorine (chloride, actually) is roughly the same. With regional and local deviations, of course.
Second argument: Plants require sulfur in half that volume [molar] relative to phosphorus. Quite a little. While chlorine is a microelement but plants normally contain more chlorides than magnesium or calcium. Chlorides serve keeping ionic, electric and osmotic balance of plants' fluids. Yes, they may be replaced by other species (nitrates, or anions of simple organic acids), that's why this function of chlorine is not essential, but from energetic point chlorides are the "cheapest" option. In short, plants take up many times more chlorides than sulfates.

 

[MichaelJ]

First, I'm not sure whether animals perceive conductivity the way our EC meters do. My lay guess is they perceive primarily osmotic pressure.

Those are closely correlated. Higher TDS means higher osmotic pressure. The source of the TDS plays a role too for sure.

Wow. Do you know from serious source?

https://www.ams.usda.gov/sites/default/files/media/Calcium%20Chloride%201%20TR.pdf

"DowflakeTM calcium chloride dihydrate is at least 96% calcium chloride dihydrate. The major impurity is magnesium and alkali
salts <4%. Most of this is sodium chloride. Other impurities are: arsenic <3 ppm; fluoride <.004%; heavy metals <.002%;
calcium hydroxide <0.2%; and iron <0.003% (Dow, 2001)."

Does it not depend on the original matter which the chemicals are made from? Yes, everything is manufactured in China, but is really all calcium chloride in the world made in the same way from the same resource (marine water, perhaps)?

CaSO4 (Gypsom Salt) are mined from natural deposits whereas CaCl2 are manufactured.

I disagree. I've read statistics on world's freshwater sources and molar content of sulfur and chlorine (chloride, actually) is roughly the same. With regional and local deviations, of course.
Second argument: Plants require sulfur in half that volume [molar] relative to phosphorus. Quite a little. While chlorine is a microelement but plants normally contain more chlorides than magnesium or calcium. Chlorides serve keeping ionic, electric and osmotic balance of plants' fluids. Yes, they may be replaced by other species (nitrates, or anions of simple organic acids), that's why this function of chlorine is not essential, but from energetic point chlorides are the "cheapest" option. In short, plants take up many times more chlorides than sulfates.

At least in one of my tanks I haven't fed my plants chlorides for ages, so I suppose its either a non-essential micro nutrient or they get it from a source unbeknownst to me.

In support of your argument on availability, there are indeed water ways (this the Amazon) where Cl is more abundant than SO4:

Cheers,
Michael

 

[Wookii]

Hi @Wookii, This is a test I did sometime ago:

Targeting ~20 ppm of Ca in 1 US gallon (3.78L) of water:

Starting point in both tests are equal temperature pure RO-DI water with a TDS of ~2 ppm.

Test 1:
Added and dissolved 0.33 g of CaSO4.2H2O. : TDS 62 ppm (124 uS/cm).

Test 2:
Added 0.28g of CaCl2.2H2O: TDS 125 ppm (250 uS/cm).

Thanks Michael - I have to say though, those numbers don't match what I see in my tank. Now I'm home from work, checking my accurate dosing figures from the IFC Calc, I dose around 18-19ppm Calcium in my tank, along with around 6ppm Magnesium for around 4dGH. Added to that are all the ferts I dose (currently around 10ppm NO3, 1.5ppm PO4 and 7ppm K weekly).

I appreciate there may be some losses of Mg, and a tiny bit of Ca, due to plant consumption, and I can also accept that there may be differences in meter variability, but my TDS is pretty much solid at 93ppm. (188uS). Thats a full 25% lower than your test which only included a similar amount of calcium/CaCl2 and nothing else?

Interestingly, the IFC Calculator also shows a 56ppm TDS estimate from a 0.28g CaCl2 dose in 3.78 litres of RO? I know you and @Hanuman discussed this in the link you gave, but what was the conclusion - is the IFC figure not correct?

The IFC Calc actually shows 81.5ppm TDS from my target remin dosing above, so with a little ferts thrown in correlates fairly well with the 93ppm TDS I'm measuring.

(For clarification, I'm not trying to be argumentative here, I genuinely want to understand where the difference might be to ensure I'm not using erroneous numbers).

 

[MichaelJ]

Secondly, with all respect, I somewhat doubt what you say (and surely will test on the first occasion) that the same volume [molar] of CaCl2 will increase conductivity notably more than CaSO4. My (hazy, amateurish) perception of charge density leads to an opinion that it's roughly the same.
I may be completely mistaken, of course.

When I first noticed this some years ago I thought my CaCl2 was tainted/spoiled... I bought some high grade CaCl2 and redid the test with same results and done the test one a couple of occasions since then, most lately related to this thread where @Hanuman and myself sort of had the same discussion:

CaSO4 vs CaCl2

If you want to reduce sulphate levels you can swap CaSO4 with CaCl2 (Calcium chloride). You will end up with a balanced mix of sulphates and chlorides rather than a higher amount of sulphates. My case for using CaSO4 over CaCl2 is two fold: S is an essential macro and Cl is an essential...

www.ukaps.org

Should you come to another conclusion I am all ears

Cheers,
Michael

 

[riioKen]

Ok guys, thanks to black Friday, the Myaqua 1900 can be found at 239€, seems a good price. Do you suggest me this one? Seems that its rated 1:1. About salts for reminalize ro, I have MgSO4 for Mg , while for Ca, if I got it correctly, the 2 salts that you suggested (@_Maq_, @MichaelJ and @Wookii )
One has more solubility but more TDS, the other, way less soluble but gives half tds (which seems great, considering that I would like to keep CRS)

Of course there are difference with sulphates too.

About KH, it would be possible to keep 1kh? honestly I don't that I would be able to maintain 1kh stable due to fresh aqua soil

 

[riioKen]

So when you change the second 65 litres, you are effectively changing out 23% of the 65 litres you just changed, so the effective total water change is only 115 litres (41%). If you did a third consecutive water change, you'd be effectively changing 153 litre (55%).

I've even found a spot where I can place a 150L container

 

[Hanuman]

Interestingly, the IFC Calculator also shows a 56ppm TDS estimate from a 0.28g CaCl2 dose in 3.78 litres of RO? I know you and @Hanuman discussed this in the link you gave, but what was the conclusion - is the IFC figure not correct?

TDS values in the IFC calculator are theoretically correct as far as I am aware. We get the same results as with the Lenntech website. TDS and Electrical Conductivity - Lenntech

I think the issue stems from our TDS meters and the convertion factors of our pens. Better put, some ions differ as electrical conductors and thus our pens show slightly different values than the theoratical values. So this is a situation where theory and reality do not meet.
You also need to take into account multiple other factors, such as full solubility of the salt, contamination and compounds current hydration. For instance, CaCl2 will inevitably suck up water with time increasing its weight and leading to erroneous weighing, thus decreasing Ca content in water as well as TDS, assuming no other comtaminants enter into play.

To conclude, takes those TDS calculations with a grain a salt.

Calcium Sulfate (gypsum) CaSo4.2H2O

This is a question for the chemists or those who have anchored experienced in chemistry. I am experiencing so odd situation. I bought some Calcium Sulfate CaSo4.2H2O as can be seen in picture below. I have been having some trouble defining the exact dose for my tank. I assumed my tank was...

www.ukaps.org

The influence of ion composition of water on its electrical conductivity

tiwater.info

 

[MichaelJ]

Thanks Michael - I have to say though, those numbers don't match what I see in my tank. Now I'm home from work, checking my accurate dosing figures from the IFC Calc, I dose around 18-19ppm Calcium in my tank, along with around 6ppm Magnesium for around 4dGH. Added to that are all the ferts I dose (currently around 10ppm NO3, 1.5ppm PO4 and 7ppm K weekly).

I appreciate there may be some losses of Mg, and a tiny bit of Ca, due to plant consumption, and I can also accept that there may be differences in meter variability, but my TDS is pretty much solid at 93ppm. (188uS). Thats a full 25% lower than your test which only included a similar amount of calcium/CaCl2 and nothing else?

Interestingly, the IFC Calculator also shows a 56ppm TDS estimate from a 0.28g CaCl2 dose in 3.78 litres of RO? I know you and @Hanuman discussed this in the link you gave, but what was the conclusion - is the IFC figure not correct?

The IFC Calc actually shows 81.5ppm TDS from my target remin dosing above, so with a little ferts thrown in correlates fairly well with the 93ppm TDS I'm measuring.

The conductivity is mostly what correlates to osmotic pressure so thats what we are really concern about. In general, fish adapted to low EC (the soft water fish we mostly keep) will have to disperse a lot more energy in a high EC environment to maintain their salt balance, breathe and survive basically. At extreme levels this will result in osmotic stress and make them more subjective to illness, organ failure etc. To some extent I think our soft water plants are not necessarily that much different... but I don't have much to back up that idea. At least for Hydroponics there appears to be something to it.

Now, the whole translation from ppm's of compounds we add to our tank into TDS (or EC) is a bit confusing. I am certainly not a chemist so any further clarification will definitely help me understand this better... But here goes my understanding of the situation: Depending on the compound we dilute the ppm concentration will only roughly and sometimes badly translate into equal TDS ppm's. This is due to the varying conductivity (ionic charge essentially) among the elements we are adding, for instance Magnesium is 0.226 10^6/cm Ω and Calcium is 0.298 10^6/cm Ω . (the difference can be much larger for other elements such as Sulphur is only 5.0x10^-24 10^6/cm Ω, .... ). So in practical terms, due to the fact that our TDS meter is measuring the conductivity and convert that into a ppm value rather than the actual ppm - a measurement that can only be done precisely using gravimetric analysis (think lab equipment) - we get only a rough approximation with our TDS meters... The only ~100% match you will ever get between the ppm of a diluted compound is the reference frame for your TDS meter. Say, if your reference (calibration fluid) is KCL. any concentration of KCL will give you an EC measurement that accurately correspond to the actual ppm of that solution (subject to the measurement error of the device). Anyway, this is my understanding.. A more elaborate summing up goes along these lines.

(For clarification, I'm not trying to be argumentative here, I genuinely want to understand where the difference might be to ensure I'm not using erroneous numbers).

For sure @Wookii, I wish to understand this better as well. The only approach that works for me is to submit my understanding and have more knowledgeable people poke holes in it … I’m not an authority by any stretch of the imagination.

Cheers,
Michael

 

[Hanuman]

I appreciate there may be some losses of Mg, and a tiny bit of Ca, due to plant consumption, and I can also accept that there may be differences in meter variability, but my TDS is pretty much solid at 93ppm. (188uS). Thats a full 25% lower than your test which only included a similar amount of calcium/CaCl2 and nothing else?

Interestingly, the IFC Calculator also shows a 56ppm TDS estimate from a 0.28g CaCl2 dose in 3.78 litres of RO? I know you and @Hanuman discussed this in the link you gave, but what was the conclusion - is the IFC figure not correct?

TDS values in the IFC calculator are theoretically correct as far as I am aware. We get the same results as with the Lenntech website. TDS and Electrical Conductivity - Lenntech

I think the issue stems from our TDS meters and the convertion factors of our pens. Better put, some ions differ as electrical conductors and thus our pens show slightly different values than the theoratical values. So this is a situation where theory and reality do not meet.
You also need to take into account multiple other factors, such as full solubility of the salt, contamination and compounds current hydration. For instance, CaCl2 will inevitably suck up water with time increasing its weight and leading to erroneous weighing, thus decreasing Ca content in water as well as TDS, assuming no other comtaminants enter into play.

To conclude, takes those TDS calculations with a grain a salt.

Calcium Sulfate (gypsum) CaSo4.2H2O

This is a question for the chemists or those who have anchored experienced in chemistry. I am experiencing so odd situation. I bought some Calcium Sulfate CaSo4.2H2O as can be seen in picture below. I have been having some trouble defining the exact dose for my tank. I assumed my tank was...

www.ukaps.org

The influence of ion composition of water on its electrical conductivity

tiwater.info

I looked at the tests I did in the past.

TDS values between the IFC Calculator and the actual value I obtained from my TDS pen where pretty much the same (830ppm calculated vs 835ppm measured) for CaCl₂ (Calcium Chloride Anhydrous). This is after I heated up the CaCl₂∙2H₂O (Calcium Chloride Dihydrate) I had to make sure I was working with anhydrious CaCl₂ and avoid any descrenpencies. So @Wookii , make sure you select the correct hydrate in the CoreSettings sheet and also make sure that what you are adding in your tank is the hydrate you selected. As I said in the link above:

CaCl₂ is really problematic due to its hygroscopic property. You really need to keep that compound locked up somewhere hermetically else it just sucks up all the water around and will end up dropping your GH with time.

I can't say the same thing for CaSO₄∙2H₂O where there was a ~350ppm descrenpency between calculated (1020 ppm) and measured (663 ppm) TDS values. I am not entirely sure why this is, but it is possible that the Calcium Sulphate I have has taken moisture from the air and therefore skewed the results but normally CaSO₄∙2H₂O is more stable than CaCl₂ so my preliminary conclusion here is that the calcium-sulpahte pair conductivity is not being fully picked up by the pen so to speak. @dw1305 @X3NiTH please correct me if I am wrong as I am making asusmptions here.
It is also possible my CaSO₄∙2H₂O is not what I think it is. I would need to redo this test with brand new CaSO₄∙2H₂O or by heating up the CaSO₄∙2H₂O I have, although I am not sure if the later will result in proper CaSO₄ (anhydrous) which can be used for a test.

 

[_Maq_]

The discussion on osmotic pressure began with comparing sulfates and chlorides.
To avoid issues with calcium sulfate solubility, I suggest comparing magnesium salts. MgSO4 vs. MgCl2.

 

[dw1305]

Hi all,

I suggest comparing magnesium salts. MgSO4 vs. MgCl2.

That sounds a sensible conclusion.

I can't say the same thing for CaSO₄∙2H₂O where there was a ~350ppm descrenpency between calculated (1020 ppm) and measured (663 ppm) TDS values. I am not entirely sure why this is, but it is possible that the Calcium Sulphate I have has taken moisture from the air and therefore skewed the results but normally CaSO₄∙2H₂O is more stable than CaCl₂ so my preliminary conclusion here is that the calcium-sulpahte pair conductivity is not being fully picked up by the pen so to speak. @dw1305 @X3NiTH please correct me if I am wrong as I am making asusmptions here.
It is also possible my CaSO₄∙2H₂O is not what I think it is. I would need to redo this test with brand new CaSO₄∙2H₂O or by heating up the CaSO₄∙2H₂O I have, although I am not sure if the later will result in proper CaSO₄ (anhydrous) which can be used for a test.

The conductivity meter just measures the electrical current conducted by the ions in solution, so if the calcium sulphate (CaSO4.nH2O) was fully disassociated into ions? Those ions would be exactly the same as any other Ca++ and SO4-- ions.

So you either have:

• the calcium sulphate (CaSO4.2H2O) was not fully dissolved (the solubility is only about 2g per litre), or
• with a higher degree of hydration than you thought you had (so not 2CaSO4.H2O).

I think heating will give you "Plaster of Paris" (2CaSO4.H2O), rather than the anhydrous salt (CaSO4). You could actually try chilling the solution <"Calcium sulfate - Wikipedia">,

....The dissolution of the different crystalline phases of calcium sulfate in water is exothermic and releases heat (decrease in Enthalpy: ΔH < 0). As an immediate consequence, to proceed, the dissolution reaction needs to evacuate this heat that can be considered as a product of reaction. If the system is cooled, the dissolution equilibrium will evolve towards the right according to the Le Chatelier principle and calcium sulfate will dissolve more easily. Thus the solubility of calcium sulfate increases as the temperature decreases and vice versa....

cheers Darrel

 

[riioKen]

Ok guys, I bought and installed the Myaqua 1900.

Today I did the first water change,
65L container, I've used IFC, but something is a bit off.

RO water tds is 20ppm.
On IFC calculator (I've made a mistake, I've used values for a 72L WC, instead I did a 65L WC) I set the ratio between Ca and Mg, i.e. 3:1 for a total GH of 5, IFC shows me that with a GH of 5, the TDS should be 114ppm.

So, ro water is 20ppm, the GH gives me 114ppm, I was expecting something like 135, even 150 was ok for me, but the result, after added 5,56g of MgSO4 and 7,19 CaSO4, is 270ppm.

What happened?

@Hanuman Sorry for tagging you, what do you think? I have made a mistake?

The TDS I've used is the one that came with the ro unit from Arka

Edit: I've measured GH from ro with the salts added, it's 8.5 instead of 5, is possible that 1g difference gives 120ppm increase value?

I've checked values from rotala butterfly too, and the result in grams is even higher (with a 65L container) that the one I've used


Edit2: I have reread the entire thread, seems that what happened to me, it's the same that happened to @Hanuman in the his thread few comments above. In facts after adding MgSO4, the tds went from 20ppm to 70ish, and only after adding CaSO4 it skyrocketed to almost 300ppm

The salts are CaSO4 dihydrate and MgSO4 hepta

 

[MichaelJ]

Ok guys, I bought and installed the Myaqua 1900.

Today I did the first water change,
65L container, I've used IFC, but something is a bit off.

RO water tds is 20ppm.
On IFC calculator (I've made a mistake, I've used values for a 72L WC, instead I did a 65L WC) I set the ratio between Ca and Mg, i.e. 3:1 for a total GH of 5, IFC shows me that with a GH of 5, the TDS should be 114ppm.

So, ro water is 20ppm, the GH gives me 114ppm, I was expecting something like 135, even 150 was ok for me, but the result, after added 5,56g of MgSO4 and 7,19 CaSO4, is 270ppm.

What happened?

@Hanuman Sorry for tagging you, what do you think? I have made a mistake?

The TDS I've used is the one that came with the ro unit from Arka

Edit: I've measured GH from ro with the salts added, it's 8.5 instead of 5, is possible that 1g difference gives 120ppm increase value?

I've checked values from rotala butterfly too, and the result in grams is even higher (with a 65L container) that the one I've used


Edit2: I have reread the entire thread, seems that what happened to me, it's the same that happened to @Hanuman in the his thread few comments above. In facts after adding MgSO4, the tds went from 20ppm to 70ish, and only after adding CaSO4 it skyrocketed to almost 300ppm

The salts are CaSO4 dihydrate and MgSO4 hepta

Don't use a TDS meter to dial in or verify your actual GH. For that you use a reagent such as the API GH/KH kit. You can use the TDS meter to test consistency - say you measure a dGH of 6 with a test kit and some ppm value with your TDS meter - whatever that is (as explained in the posts above - this value will vary depending on your calibration reference, the EC strength of the electrolytes your mixing and not the actual ppm) - you can however write down the value and use it as a sanity check of your remineralization.

If you add 7.19 grams of CaSO4 to 65 L of RO water you will get ~26 ppm of Ca which amounts to 3.6 dGH
If you add 5.56 grams of MgSO4 to 65 L of RO water you will get ~8.5 ppm of Mg which amounts to ~2 dGH

So your total dGH in the WC water your blending will be 5.6 dGH. Thats it.

If your TDS meter in fact tells you its almost 300 ppm in the mixing container after ONLY adding the above mentioned amounts of salts your TDS meter is either off or your salts are contaminated / spoiled...

Your RO water TDS sounds a bit high at 20 ppm - not abnormally so, but you may want to re-calibrate the meter just in case.

Cheers,
Michael