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Discussion Starter · #1 ·
This will be a short journal. I got a TDS pen a few months ago and found out my tank's TDS using tap water is 510 ppm. Using RO water reduced the TDS to 310 ppm. This seems pretty good to me but I want to go lower. My goal is to break the 200 ppm barrier. There are only 110 ppm left to eliminate to achieve this goal. This shouldn't be too hard. The only constraint is that the RO water has to be remineralized to 6 dGH for Otocinclus and Amano Shrimp.

The first part of the plan is to use Magnesium Nitrate to replace some of the Magnesium Sulfate I use to remineralize RO water. I'm going to use enough MgNO3 to get 15 ppm NO3 out of it. Then I'll use MgSO4 if I need any more Magnesium. I will take NO3 out of my macro dosing solution. The macro solution will just have Phosphate and Potassium in it.

The second part of the plan is to once again try to dissolve 1 dGH CaCO3 in RO water. This will be my third attempt. This time I plan on using 2 ml Muriatic Acid in 5 gallons of RO water to see if the CaCO3 will dissolve. I watched a video about using Muriatic Acid for Discus on Youtube. It takes three days for the water to be safe to use. But hey, maybe the CaCO3 will make it go faster.

This is all just an experimental project for the time being. I don't think I'll be throwing any Muriatic Acid water into my tank anytime soon. I called the Malinckrodt Chemical Company today to find Magnesium Nitrate. But then I saw it's sold on Amazon. I went to the hardware store and bought some Muriatic Acid. I went to storage and found my Calcium Carbonate. Then I went to the water store and got 5 gallons of RO water.

Ultimately, I might be looking at setting up a water treatment container of some kind. I'm thinking about getting a 20 to 30 gallon food grade drum. I already have a powerhead I can use to mix the water. This weekend I'll start working on the calculations to see how much using MgNO3 will reduce TDS. Feel free to chime in if you have any ideas.

I would like to thank @Immortal1 for inspiring this project with one of his posts in the archive.
 

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Any particular reason to use CaCO3 to raise the KH?

If you are only looking to remin RO to 6 dGH then you could use CaSO4.2H2O and MgSO4 (Epsom salt) to get a 3:1 or 4:1 ratio of Ca to Mg and use this to raise the dGH to 6. The TDS would be around 180-200.


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Discussion Starter · #3 · (Edited)
Any particular reason to use CaCO3 to raise the KH?

If you are only looking to remin RO to 6 dGH then you could use CaSO4.2H2O and MgSO4 (Epsom salt) to get a 3:1 or 4:1 ratio of Ca to Mg and use this to raise the dGH to 6. The TDS would be around 180-200.


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I should be able to dissolve 17.6 mg/l of CaCO3. I forget at what pH and temperature. You can actually dissolve more of it at cooler temperatures. This would reduce the TDS because I would be able to use less CaSO4 and avoid using some unnecessary Sulfate. 77.5% of CaSO4 is Sulfate [sic]. There will be Sulfate free Calcium If I can break the CO3 off of its Calcium. I have tried dissolving CaCO3 before but it never works even at 17.6 mg/l. I won't use it if it doesn't dissolve.

Mixing CaSO4 and MgSO4 is what I am doing now. I don't know why the TDS in the tank is 310 ppm. The water I am using s 6.6 dGH because I used measuring spoons instead of a scale resulting in 8.3 dGH which I diluted down to the 6.6. One lesson that I have learned is that you have to be really accurate at this. So I'll use the scale and get it right. Incidently, the KH is 2 degrees. Whatever amount of TDS that that adds.

That 3:1 to 4:1 Ca:Mg ratio you mention will be important in order to optimize reducing the TDS. I'll put some numbers up. I love doing that. Unfortunately, It really turns people off, which is why I'm putting this in a journal. I won't be trespassing on somebody's thread with boring calculations this way.

EDIT: 37.17% of CaSO4.2H2O is Sulfate.
 
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Thanks for your explanation, re-read the post against and understood your goals better. Following this thread.

Question: what’s bad about sulfate accumulation in the tank? What I have read is that plants need sulphur in small amounts. But I wanted to understand the impact of more than required amount of sulphur on plant growth and animal health.


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My comments will ignore the issue of whether or not a TDS reading (presumably 500 scale) of 310 is good or bad and will just focus upon answering your questions. I’m also ignoring any desired targeting of alkaline buffer (KH), since you didn’t mention it.

First, you might find this calculator to make it a little easier to perform sensitivity analysis on the ppm of all of your salts in one view: PPM Calculator. You would perform your calculations for individual salts on the likes of the Zorfox or RotalaButterfly calculators, then plug the resulting ppm of each element into this "PPM Calculator."

Make sure that you aren’t starving your plants for sulfate and be careful about causing too great a change in the pH of your tank water when you add your water. As you know, ph changes from CO2 have no effect upon fish, but strong acids can drop pH pretty low and a large change of this type of acidity can harm some species if it is too sudden. I would target a pH of about 6, in your batch water, when adding the strong acids.

Regarding calcium, although you are pushing against the upper solubility limits of CaCO3 (or MgCO3) you should be able to dissolve 1 dKH’s worth in acidic water, but doing so in a pre-tank batch of RO water will require the use of the strong acid, as you know. I find it easier to add the powder to my tank, which always has a pH in the 5.6-6.0 area. This may work for you as well, and then you don’t have to play with the strong acids. You could also use Ca gluconate, which is, essentially, pure Ca and dissolves easily.
 

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Discussion Starter · #6 ·
My comments will ignore the issue of whether or not a TDS reading (presumably 500 scale) of 310 is good or bad and will just focus upon answering your questions. I’m also ignoring any desired targeting of alkaline buffer (KH), since you didn’t mention it.

First, you might find this calculator to make it a little easier to perform sensitivity analysis on the ppm of all of your salts in one view: PPM Calculator. You would perform your calculations for individual salts on the likes of the Zorfox or RotalaButterfly calculators, then plug the resulting ppm of each element into this "PPM Calculator."

Make sure that you aren’t starving your plants for sulfate and be careful about causing too great a change in the pH of your tank water when you add your water. As you know, ph changes from CO2 have no effect upon fish, but strong acids can drop pH pretty low and a large change of this type of acidity can harm some species if it is too sudden. I would target a pH of about 6, in your batch water, when adding the strong acids.

Regarding calcium, although you are pushing against the upper solubility limits of CaCO3 (or MgCO3) you should be able to dissolve 1 dKH’s worth in acidic water, but doing so in a pre-tank batch of RO water will require the use of the strong acid, as you know. I find it easier to add the powder to my tank, which always has a pH in the 5.6-6.0 area. This may work for you as well, and then you don’t have to play with the strong acids. You could also use Ca gluconate, which is, essentially, pure Ca and dissolves easily.
My TDS reading is probably 500 scale. The instrument measures a combination pH, Salinity, Conductivity, TDS and temperature. So I'm assuming, maybe incorrectly, that it's the 500 Sodium scale since the instrument measures salinity. I could call LaMotte technical support and ask them. It might also be in the user manual. I am currently targeting 2 dKH with Potassium Bicarbonate.

Sulfate is not something I test for. It never occurred to me that I could run low on it. I thought I could lower the TDS by reducing some of it. I don't think my Muriatic Acid trial to dissolve CaCO3 is going to pan out. Jack Wattley Discus has a good video on Youtube about how to use Muriatic Acid to lower pH. The two things I learned from the video are that it takes a very small amount of the acid to lower the pH and that you should wait 72 hours before using the water.

I have not been able to dissolve even 17.6 mg/l of CaCO3 trying to prepare RO water. It will dissolve over the long term if you put it in your tank. It just takes time for acids to react with the CO3. When it comes to preparing RO water, I think about 2 ml Muriatic Acid in 5 gallons of water should just about do it. It's a starting point anyway.


I calculated four different combinations of salts to see how much TDS can be reduced. I thought the substitution of CaCO3, CaCl2 and MgNO3 for CaSO4 and MgSO4 would reduce Sulfate and consequently TDS. This turned out not to be true. The TDS reduction resulting in these substitutions is not substantial. In fact, the standard CaSO4 MgSO4 GH booster recipe causes less TDS than the other recipes. I'm not even sure it would be worth it to use CaCO3 . It doesn't seem to help much.

6 dGH 18.925 l CaSO4 MgSO4
2,357 mg CaSO4.2H2O {29.0 & 46.3 ppm Ca & SO4}
1,856 mg MgSO4.7H2O {9.67 & 25.47 ppm Mg & SO4}
TDS = 110.44 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

6 dGH 18.925 l CaSO4 MgNO3 MgSO4
2,357 mg CaSO4.2H2O {29.0 & 46.3 ppm Ca & SO4}
587 mg MgNO3.6H2O {2.94 & 15 ppm Mg & NO3}
1,291 mg MgSO4.7H2O {6.73 & 17.73 ppm Mg & SO4}
TDS = 117.70 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

6 dGH 18.925 l CaCO3 CaSO4 MgNO3 MgSO4
334 mg CaCO3 {7.14 & 10.53 ppm Ca & CO3}
1,777 mg CaSO4.2H2O {21.86 & 34.9 ppm Ca & SO4}
587 mg MgNO3.6H2O {2.94 & 15 ppm Mg & NO3}
1,291 mg MgSO4.7H2O {6.73 & 17.93 ppm Mg & SO4}
TDS = 117.03 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

6 dGH 18.925 l CaCO3 CaSO4 CaCl2 MgNO3 MgSO4
334 mg CaCO3 {7.14 & 10.53 ppm Ca & CO3}
888 mg CaSO4.2H2O {10.93 & 17.45 ppm Ca & SO4}
573 mg CaCl2 {10.93 & 19.34 ppm Ca & Cl}
587 mg MgNO3.6H2O {2.94 & 15 ppm Mg & NO3}
1,291 mg MgSO4.7H2O {6.73 & 17.73 ppm Mg & SO4}
TDS = 118.72 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

Ingredients
CaCO3
Ca 40.04%
CO3 59.96%

CaSO4.2H2O
Ca 23.28%
SO4 37.17%

CaCl2
Ca 36.11%
Cl2 63.89%

MgSO4.7H2O
Mg 9.86%
SO4 25.97%

MgNO3.6H20
Mg 9.48%
NO3 48.36%

7.144 mg/l Ca = 1 dGH
4.355 mg/l Mg = 1 dGH

I thought I found a good source of MgNO3.6H2O on Amazon but it turned out to be Mg(NO3)2 which is somethinng different. I then called around to several local hydroponics stores to see if they have MgSO4.6H2O powder and nobody has it. There are also a couple of more suspect products on the internet for MgNO3 to culture bacteria. I'm just not sure how much I trust these sites with my credit card number.

A company named Avantor sells a 1 kg ACS grade crystaline MgNO3.6H2O made by Spectrum Chemical for $150.00 which I would have to pick up at my local chemical supplier. Avantor also sells a 500 g ACS grade flake MgNO3.6H2O for only $30.00. JT Baker makes a 500 g ACS grade MgNO3.6H2O for $112.80. It looks like flake is the way to go.

Given the calculated GH booster recipes above, It looks like substituting MgNO3 for MgSO4 will only reduce TDS by at most 15 ppm because of the NO3 substitution for SO4. Is it worth the expense and extra effort to reduce TDS by such a small amount? One of the conclusions I make from these calculations is that I will have to use my sensitive Ohaus scale to weigh my GH booster. A scale works to help my dog lose weight. Maybe it will work to reduce TDS.

Next weekend I will post some test results. I might not have the MgNO3.6H2O by then but maybe I can see where I currently stand with the GH and TDS in the remineralized water that i'm using. I know the TDS in the tank is 310 ppm. I also need to get a new container in which to try to dissolve CaCO3. Either that, or scale down to a two gallon bucket.
 
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Discussion Starter · #7 ·
Thanks for your explanation, re-read the post against and understood your goals better. Following this thread.

Question: what’s bad about sulfate accumulation in the tank? What I have read is that plants need sulphur in small amounts. But I wanted to understand the impact of more than required amount of sulphur on plant growth and animal health.


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There's nothing bad about Sulfate accumulation in the tank. Dr. Barr says it can accumulate up to 200 ppm and not cause a problem. I'm just looking at reducing Sulfate as a way to reduce TDS. I don't have a problem with Sulfate otherwise. Maybe I should get a Sulfate test for my colorimeter. That might be interesting. LaMotte makes a high range Sulfate test that measures between 3 to 100 ppm Sulfate. The test sample can be diluted to measure higher ranges. Sulphur is listed as a macro nutrient on 2hraquarist.com.
 
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My TDS reading is probably 500 scale. The instrument measures a combination pH, Salinity, Conductivity, TDS and temperature. So I'm assuming, maybe incorrectly, that it's the 500 Sodium scale since the instrument measures salinity. I could call LaMotte technical support and ask them. It might also be in the user manual. I am currently targeting 2 dKH with Potassium Bicarbonate.

Sulfate is not something I test for. It never occurred to me that I could run low on it. I thought I could lower the TDS by reducing some of it. I don't think my Muriatic Acid trial to dissolve CaCO3 is going to pan out. Jack Wattley Discus has a good video on Youtube about how to use Muriatic Acid to lower pH. The two things I learned from the video are that it takes a very small amount of the acid to lower the pH and that you should wait 72 hours before using the water.

I have not been able to dissolve even 17.6 mg/l of CaCO3 trying to prepare RO water. It will dissolve over the long term if you put it in your tank. It just takes time for acids to react with the CO3. When it comes to preparing RO water, I think about 2 ml Muriatic Acid in 5 gallons of water should just about do it. It's a starting point anyway.


I calculated four different combinations of salts to see how much TDS can be reduced. I thought the substitution of CaCO3, CaCl2 and MgNO3 for CaSO4 and MgSO4 would reduce Sulfate and consequently TDS. This turned out not to be true. The TDS reduction resulting in these substitutions is not substantial. In fact, the standard CaSO4 MgSO4 GH booster recipe causes less TDS than the other recipes. I'm not even sure it would be worth it to use CaCO3 . It doesn't seem to help much.

6 dGH 18.925 l CaSO4 MgSO4
2,357 mg CaSO4.2H2O {29.0 & 46.3 ppm Ca & SO4}
1,856 mg MgSO4.7H2O {9.67 & 25.47 ppm Mg & SO4}
TDS = 110.44 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

6 dGH 18.925 l CaSO4 MgNO3 MgSO4
2,357 mg CaSO4.2H2O {29.0 & 46.3 ppm Ca & SO4}
587 mg MgNO3.6H2O {2.94 & 15 ppm Mg & NO3}
1,291 mg MgSO4.7H2O {6.73 & 17.73 ppm Mg & SO4}
TDS = 117.70 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

6 dGH 18.925 l CaCO3 CaSO4 MgNO3 MgSO4
334 mg CaCO3 {7.14 & 10.53 ppm Ca & CO3}
1,777 mg CaSO4.2H2O {21.86 & 34.9 ppm Ca & SO4}
587 mg MgNO3.6H2O {2.94 & 15 ppm Mg & NO3}
1,291 mg MgSO4.7H2O {6.73 & 17.93 ppm Mg & SO4}
TDS = 117.03 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

6 dGH 18.925 l CaCO3 CaSO4 CaCl2 MgNO3 MgSO4
334 mg CaCO3 {7.14 & 10.53 ppm Ca & CO3}
888 mg CaSO4.2H2O {10.93 & 17.45 ppm Ca & SO4}
573 mg CaCl2 {10.93 & 19.34 ppm Ca & Cl}
587 mg MgNO3.6H2O {2.94 & 15 ppm Mg & NO3}
1,291 mg MgSO4.7H2O {6.73 & 17.73 ppm Mg & SO4}
TDS = 118.72 ppm
29.00 Ca 9.67 Mg; 3 Ca:1 Mg

Ingredients
CaCO3
Ca 40.04%
CO3 59.96%

CaSO4.2H2O
Ca 23.28%
SO4 37.17%

CaCl2
Ca 36.11%
Cl2 63.89%

MgSO4.7H2O
Mg 9.86%
SO4 25.97%

MgNO3.6H20
Mg 9.48%
NO3 48.36%

7.144 mg/l Ca = 1 dGH
4.355 mg/l Mg = 1 dGH

I thought I found a good source of MgNO3.6H2O on Amazon but it turned out to be Mg(NO3)2 which is somethinng different. I then called around to several local hydroponics stores to see if they have MgSO4.6H2O powder and nobody has it. There are also a couple of more suspect products on the internet for MgNO3 to culture bacteria. I'm just not sure how much I trust these sites with my credit card number.

A company named Avantor sells a 1 kg ACS grade crystaline MgNO3.6H2O made by Spectrum Chemical for $150.00 which I would have to pick up at my local chemical supplier. Avantor also sells a 500 g ACS grade flake MgNO3.6H2O for only $30.00. JT Baker makes a 500 g ACS grade MgNO3.6H2O for $112.80. It looks like flake is the way to go.

Given the calculated GH booster recipes above, It looks like substituting MgNO3 for MgSO4 will only reduce TDS by at most 15 ppm because of the NO3 substitution for SO4. Is it worth the expense and extra effort to reduce TDS by such a small amount? One of the conclusions I make from these calculations is that I will have to use my sensitive Ohaus scale to weigh my GH booster. A scale works to help my dog lose weight. Maybe it will work to reduce TDS.

Next weekend I will post some test results. I might not have the MgNO3.6H2O by then but maybe I can see where I currently stand with the GH and TDS in the remineralized water that i'm using. I know the TDS in the tank is 310 ppm. I also need to get a new container in which to try to dissolve CaCO3. Either that, or scale down to a two gallon bucket.
Although I haven't used it for a while, the Mg(NO3) that I used was purchased at GLA, and it is inexpensive.
 

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Discussion Starter · #9 ·
Although I haven't used it for a while, the Mg(NO3) that I used was purchased at GLA, and it is inexpensive.
I think GLA discontinued their MgNO3. I've looked more than once. There must not have been enough demand for it. It straddles the line between a GH booster and a fertilizer. I've considered it in the past but I didn't understand what it does. I thought it was exotic and unnecessary. But it can shave a few points off your TDS if you use it. GH was 6.28 degrees last week. It was pretty close to my target of 6 degrees. TDS was 340 ppm up 30 points. I think the high TDS might be caused by the Fluorite mixed in my gravel. This is going to be an interesting puzzel to solve.
 

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I dunno, if it were me, I'd go back to figuring out why your TDS is in the 300s to begin with when you're using RO water. If your GH/Kh is only responsible for about a third of that, then I would look at what else is adding to it. Are you adding buffers or something else? How much are your other plant nutrients adding? I don't see all this ion swapping as getting you anywhere.

If you aren't sure, you might consider mixing a small batch of water, measuring TDS after you add each component so you can see for yourself where your "budget" is going.
 

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Discussion Starter · #12 ·
I dunno, if it were me, I'd go back to figuring out why your TDS is in the 300s to begin with when you're using RO water. If your GH/Kh is only responsible for about a third of that, then I would look at what else is adding to it. Are you adding buffers or something else? How much are your other plant nutrients adding? I don't see all this ion swapping as getting you anywhere.

If you aren't sure, you might consider mixing a small batch of water, measuring TDS after you add each component so you can see for yourself where your "budget" is going.
It really is like a (TDS) budget. I've been adding 2 dKH Potassium Bicarbonate and 10 mg/l fulvic acid plus the usual fertilizers. My maintenance is weekly 50% water changes. There is a surface skimmer. I don't see this ion swapping getting me anywhere either. I had to take a look at it but it's not adding up. At least I got the weights for my next GH booster recipe. I want to put some Fluorite in a two gallon bucket with some RO water to see if the Fluorite I'm using increases TDS. I've also been thinking about setting up a small prototype tank with Fluval Stratum to see if that works better.
 
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Discussion Starter · #13 ·
The Potassium Nitrate, Calcium Nitrate and Magnesium Nitrate all have an "N" on the container. I didn't look hard enough. Thanks for the link. GLA's Magnesium Sulfate is better than the Magnesium Sulfate I bought from the pharmacy. I'm satisfied with the quality if their products.
 
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