Making my own RO salt mix - The Planted Tank Forum
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post #1 of 11 (permalink) Old 10-22-2017, 07:55 AM Thread Starter
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Making my own RO salt mix

Hi All,

I use quite a fair amount of RO water in my freshwater tanks and is mainly due to my liquid chalk in a bid to reduce the constant battle with limescale on the tank and filters.

The commercial available minerals are working out quite expensive and wondered if anyone can advise on mixing your own?

I believe I have some of the key ingredients below and should be suitable for fish & shrimp.. before you ask, I have tried mixing tap/to but have never come up with the correct GH/KH I expected... TDS isnít too much of an issue at 290 but the GH is 19/KH 9. I am looking for a KH of 4 and GH of 6.

Anyway, here is what I think is the recipe :

Calcium Sulphate (CaSO4)
Magnesium Sulphate (MgSO4)
Potassium Sulphate (K2SO4)

Not sure of the quantity of each power tho?

Any help would be appreciated..

Thanks,
Chris


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post #2 of 11 (permalink) Old 10-22-2017, 12:34 PM
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What I think makes sense to me is use the CaSo4 and the MgSo4 to remineralize one gallon to the level desired. Then you would know the ratios needed. Not sure about adding the potassium


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post #3 of 11 (permalink) Old 10-22-2017, 07:59 PM
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You can mix the calcium and magnesium in in a 4 to 1 ratio (4 parts calcium by volume to one part magnesium) (NaCL, common table salt). I would add about 1/4 of the magnesium volume. This would supply all the needed Mix thoroughly. This will supply all the calcium, magnesium, sulfur and chlorine needed. and add enough to your tank reach your GH target. Most people keep the Gh between 4 or 6. I would not recommend going below 3

If you then dose the tank to 10-15ppm nitrate and 1PPM phosphate, you will have enough nitrate and phosphate and potassium. The common chemicals used for this are potassium nitrate (KNO3) and potassium phosphate (KH2Po4). If you then add a trace fertilizer (CSM+B is a good choice) you should have all minerals plants and shrimp need in the water. You can use this fertilizer calculator to figure out the correct amount to add to your tank:https://rotalabutterfly.com/nutrient-calculator.php

Note for the nail I use Morton iodized table salt. There is no harmful anti caking additives and shrimp do need a small amount of iodine in the water for good health. Although rare iodine deficiency can occur in RO tanks. and I iodize salt would help prevent that.
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post #4 of 11 (permalink) Old 10-22-2017, 09:09 PM
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Quote:
Originally Posted by tayloss View Post
I am looking for a KH of 4 and GH of 6.

Anyway, here is what I think is the recipe :

Calcium Sulphate (CaSO4)
Magnesium Sulphate (MgSO4)
Potassium Sulphate (K2SO4)
Not sure of the quantity of each power tho?
You are unlikely to get CaSO4 or MgSO4. You are far more likely to get the hydrated forms of these substances : CaSO4*2H2O and MgSO4*7H2O . You need to account for existing H2O when making further calculation. If you want a 4:1 Ca:Mg ratio by weight, this does not correspond to the CaSO4:MgSO4 and even less to CaSO4*2H2O:MgSO4*7H2O. A widely used mix to increase the GH claims a 4:1 ratio but fails to take into account the hydration of the substances.

As such for 100L
adding 13g CaSO4*2H2O and 8gMgSO4*7H2O you will have
~30mg/L Ca and ~8mg/L Mg with a total GH of ~6įdGH

To get a KH of 4 you will need a carbonate source such as NaHCO3
for 100 L adding 12g NaHCO3 will give you a KH of 4įdGH

K (from K2SO4) is not part of a GH measurement. Seachem Equilibrium has it in its remineralization salt so it was carried over. K is needed by plants but if doing EI you are likely adding enough.

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Originally Posted by Surf View Post
I would add about 1/4 of the magnesium volume.
I do not know of a commonly used way to measure/dose a cation on its own by volume. The perceived volume of a salt depends on how fine are the particles. I am not singling you out Surf, but the practice of measuring salts (dry ferts) by teaspoons is something that belongs in a Fred Flinstone episode. If you aim for a given mg/L (~ppm) you need the weight of the solute (dry fert) and volume of the solution. We have the technology. We should stop recommending the dosing and use of teaspoons as measuring units for fertilizers.
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Last edited by dukydaf; 10-22-2017 at 09:52 PM. Reason: 12
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post #5 of 11 (permalink) Old 10-23-2017, 07:02 AM
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Quote:
I do not know of a commonly used way to measure/dose a cation on its own by volume. The perceived volume of a salt depends on how fine are the particles. I am not singling you out Surf, but the practice of measuring salts (dry ferts) by teaspoons is something that belongs in a Fred Flinstone episode. If you aim for a given mg/L (~ppm) you need the weight of the solute (dry fert) and volume of the solution. We have the technology. We should stop recommending the dosing and use of teaspoons as measuring units for fertilizers.
Yes you can account for all of that but does it need to be that accurate a mix? The calcium magnesium level can and does very quite a lot in nature seasonally. Furthermore if you calculate exactly how much is need for a given amount of nitrate added you find the tank only need about 1 degree for plants. I don't know exactly how much shrimp needs but people are seeing reproduction in a wide variety of GH values. The method I used in making my own has worked for me has not caused any harm that I can see. But if Tayloss is concerned about this he can get Sachem equilibrium which is similar.

Quote:
To get a KH of 4 you will need a carbonate source such as NaHCO3
for 100 L adding 12g NaHCO3 will give you a KH of 4įdGH
As plants consume sulfur in the Gh booster Carbonates are generated in the water. its not a lot in my tank but it is 2 degrees. I also have some old snail shells in the aquarium which are made of calcium carbonate. if the water goes acidic these will start to dissolve and as it does it counteract the acidity. The shells stop dissolving at a PH of 7. They therefore work to prevent the pH from dropping and will not push the PH above seven. Other things in the aquarium can push the PH up above 7 and the snail shells will not stop that. But for most people sudden shift to acidic conditions are a concern. In my aquarium the PH is typically 6.5 to 7. In my experience the combination of decorative snail shells and the KH from sulfate consumption is sufficient to maintain a stable PH of 7. If you want to maintain a lower PH you might need a buffering substate or CO2 injection but those will cost a lot more to implement and may require you to remove any shells in the aquarium.
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post #6 of 11 (permalink) Old 10-23-2017, 07:45 AM Thread Starter
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Hi Both,

I appreciate you comments and take onboard everything you are saying.. is this not closely related to EI anyway where we donít have to be exact and canít be due to various factors of the home lab environment?

After doing some research Iíve found the following thatís aimed at Shrimps and lightly planted aquariums :-

Calcium Sulphate Heptahydrate - 55gm
Magnesium Sulphate (Espom Salt) MgSO4- 37gm
Potassium Sulphate (aka Sulphate Of Potash) K2SO4 - 11gm
Iron Sulphate (optional) FeSO4 - 0.30gm
Manganese Sulphate (optional) MnSO4- 0.16gm

So this goes toward my initial findings.. itís doesnít say what to expect the parameters to be, but says to mix with 500ml of RO and the add to a litre of water to find the TDS/GH/KH. Although Iím sure the optionals are for plants and wouldnít be needed for a shrimp only tank?

Perhaps for my planted it would be ideal to use it along with my micro/macro mix and extra KNO3 as I donít have any livestock in the planted tank and the premixed power is lacking in KNO3 as believe they expect fish to provide the additional ?

Chemistry isnít my strongest subject, but want to be in control of my tank and buying premixed is becoming expensive.. Iím surprise there isnít more subjects on mixing remineralisers considering the cost of salty shrimp/seachem powders that I believe contain a combination of the above?

Thanks for your help/comments..

Chris


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post #7 of 11 (permalink) Old 10-23-2017, 11:13 AM
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Quote:
Originally Posted by Surf View Post
Yes you can account for all of that but does it need to be that accurate a mix? The calcium magnesium level can and does very quite a lot in nature seasonally. Furthermore if you calculate exactly how much is need for a given amount of nitrate added you find the tank only need about 1 degree for plants. I don't know exactly how much shrimp needs but people are seeing reproduction in a wide variety of GH values..
If you want reproducible and comparable results yes. If you want a ration of 4:1 by mass, yes. If we do not want to measure, why use spoons then? Why not just use our eyes as we dose from the bag? I have used this method and it worked. Can I say what was inside and reproduce the failure or success? Never.


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Originally Posted by Surf View Post
As plants consume sulfur in the Gh booster Carbonates are generated in the water.
Could you detail on the process? I assume by sulfur you actually mean sulfates, but why would this increase the carbonates in water? Is there a reference for this process? I know some plants are able to use carbonates to generate CO2 but exchange SO4 with CO3?

Quote:
Originally Posted by Surf View Post
its not a lot in my tank but it is 2 degrees. I also have some old snail shells in the aquarium which are made of calcium carbonate. if the water goes acidic these will start to dissolve and as it does it counteract the acidity. The shells stop dissolving at a PH of 7. They therefore work to prevent the pH from dropping and will not push the PH above seven. Other things in the aquarium can push the PH up above 7 and the snail shells will not stop that. But for most people sudden shift to acidic conditions are a concern. In my aquarium the PH is typically 6.5 to 7. In my experience the combination of decorative snail shells and the KH from sulfate consumption is sufficient to maintain a stable PH of 7. If you want to maintain a lower PH you might need a buffering substate or CO2 injection but those will cost a lot more to implement and may require you to remove any shells in the aquarium.
All the things you describe above may happen but take place slowly over a long time. If you add a high % of ro water to a tank with sensitive fauna and wait for the carbonates to come from shells, some will die. If you want water with a pH below 7 just leave RODI water exposed to air. The CO2 and other gases will dissolve and lower the pH



Quote:
Originally Posted by tayloss View Post
is this not closely related to EI anyway where we donít have to be exact and canít be due to various factors of the home lab environment?

Chemistry isnít my strongest subject, but want to be in control of my tank
EI is about dosing enough nutrients so that they are non-limiting to plant growth. The approximation is in estimating the concentration that is non-limiting, not in not knowing how much you are really adding to the tank.

The mass of fertilizer that you dose using spoons will vary greatly between spoons, between salts and between users. I could have a very fine caso4 and have 2g in one teaspoon, while another more coarse will be 1.5g. We both come to the forum and say we dosed 200mg/L but we have very different results. You measure once and measure the same again yet the second time you run into a deficiency...

So to sum up if you dose using teaspoons you should say that you should not say you add 20mg/L No3 as this is false. You could say you dose somewhere between 5-60mg/L. If you want to have repeatable result weigh your solid fertilizers. If you want to compare dosage values, weigh your solid fertilizers. If you can afford a scale do the sensible thing and weigh your solid fertilizers. Be in control.



Quote:
Originally Posted by tayloss View Post
Calcium Sulphate Heptahydrate - 55gm
Magnesium Sulphate (Espom Salt) MgSO4- 37gm

Potassium Sulphate (aka Sulphate Of Potash) K2SO4 - 11gm
Iron Sulphate (optional) FeSO4 - 0.30gm
Manganese Sulphate (optional) MnSO4- 0.16
I think you mean calcium sulfate hemihydrate. Epsom salt is the heptahydrate form, aka MgSO4*7H2O. These things will influence how much you want to use. The unchelated forms of iron and manganese will quickly be taken out of solution at most aquariums pH. Thus, they will not provide any nutrition for plants.




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post #8 of 11 (permalink) Old 10-24-2017, 04:30 AM
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Quote:
I am not singling you out Surf, but the practice of measuring salts (dry ferts) by teaspoons is something that belongs in a Fred Flinstone episode.
And yet that is exactly how many peole dose there Estimative index tank.



This is from: AquaScaping World Magazine - Estimative Index Fertilization Method

The key thing you don't seem to understand is that precision is not needed and the variation due to grain size is typically not enough to make a big difference. When Tom Barr crated the Estimative index method he intended to be easy. He didn't want to make it a requirement for people to by test kits, scales or other hardware. So he just recommends some target ranges for nitrate, phosphate, and potassium and then translated that into the volume needed to add in teaspoons or tablespoons and Simple recipes people could follow for some common sized tanks. Variation that occurs due volume measurements is not enough to cause the methode to fail. It works for a lot of people. Some vendors now sell EI fertilizers in pump bottles. So instead of measuring the volume you just press the pump enough times to equal the volume of the tank. Reducing the need to measure down to just counting.

Quote:
All the things you describe above may happen but take place slowly over a long time. If you add a high % of ro water to a tank with sensitive fauna and wait for the carbonates to come from shells, some will die. If you want water with a pH below 7 just leave RODI water exposed to air. The CO2 and other gases will dissolve and lower the pH
The reaction rate for calcium carbonate in water with an acid is not slow. Just take a piece of calcium carbonate and drop it into a glass of vinegar. The reaction is very rapid. So if there is a rapid large PH drop the shells will respond at a proportional rate and stop the shift before you are even aware it is happening. The conversion of GH into KH is slow but if you have shells in the water you don't need a fast response.

As to RO water in a glass, fresh RO water from the tap comes out of the facet with a low PH not a high PH. And the PH over time will increase to 7 as CO2 and other gasses in your tap water dissipate into the air. Outgassed RO water always has a PH very close to 7.

Quote:
Could you detail on the process? I assume by sulfur you actually mean sulfates, but why would this increase the carbonates in water? Is there a reference for this process? I know some plants are able to use carbonates to generate CO2 but exchange SO4 with CO3?
Sometimes a plant need Calcium and sometimes it needs sulfur. Sometimes it needs both at the same time. So if the plant needs the sulfate form calcium sulfate but not the calcium the the calcium sulfate will be converted to Calcium hydroxide. And then the Calcium hydroxide will react with CO2 forming Calcium carbonate. If you can measure carbonate with a resolution of 1 ppm you will see that the KH of the aquarium does change over the week between water changes. It isn't much but it does happen. Calcium hydroxide is the key ingredient in cement used to make dams, sidewalks and roads.

Last edited by Surf; 10-24-2017 at 04:34 AM. Reason: grammer
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post #9 of 11 (permalink) Old 10-24-2017, 08:23 AM
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Quote:
Originally Posted by Surf View Post
Sometimes a plant need Calcium and sometimes it needs sulfur. Sometimes it needs both at the same time. So if the plant needs the sulfate form calcium sulfate but not the calcium the the calcium sulfate will be converted to Calcium hydroxide. And then the Calcium hydroxide will react with CO2 forming Calcium carbonate. If you can measure carbonate with a resolution of 1 ppm you will see that the KH of the aquarium does change over the week between water changes. It isn't much but it does happen. Calcium hydroxide is the key ingredient in cement used to make dams, sidewalks and roads.
Uh, this isn't how it happens. The calcium cations do not form calcium hydroxide which reacts with carbon dioxide. Ksp of calcium hydroxide is higher than sulfate, so the ions will still remained solubilized.

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post #10 of 11 (permalink) Old 10-26-2017, 07:55 AM
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Quote:
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The reaction rate for calcium carbonate in water with an acid is not slow. Just take a piece of calcium carbonate and drop it into a glass of vinegar. The reaction is very rapid. .
Sure, if your aquarium has vinegar in it or acetic acid in the same conc. . It would be even faster if you have HCl. It all depends in the acids available. In actual aquariums it will take a while for snail shells to provide enough carbonates, enough for the fish to experience osmotic stress.


Quote:
Originally Posted by Surf View Post
As to RO water in a glass, fresh RO water from the tap comes out of the facet with a low PH not a high PH. And the PH over time will increase to 7 as CO2 and other gasses in your tap water dissipate into the air. Outgassed RO water always has a PH very close to 7..
Pure RO water, exposed to the atmosphere will be at equilibrium with the atmosphere, where p(CO2) = 3.5x20e-4 atm. Because there is no alkalinity in Rodi water, your pH will be aprox 5.7. Google it, I know you can. There are plenty of chemistry tutorials and scientific articles that explain how this happens.

Quote:
Originally Posted by Surf View Post
Sometimes a plant need Calcium and sometimes it needs sulfur. Sometimes it needs both at the same time. So if the plant needs the sulfate form calcium sulfate but not the calcium the the calcium sulfate will be converted to Calcium hydroxide. And then the Calcium hydroxide will react with CO2 forming Calcium carbonate. If you can measure carbonate with a resolution of 1 ppm you will see that the KH of the aquarium does change over the week between water changes. It isn't much but it does happen. Calcium hydroxide is the key ingredient in cement used to make dams, sidewalks and roads.
You have some imaginative chemistry there. As water is a polar solvent it will separate the ions of Ca 2+ SO4 2-. In other words, once fully dissolved in water, it does not matter where the cation and anion comes from. The shift in KH you notice is likely to come from evaporation.

In the light of the above, I think I made my point.

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post #11 of 11 (permalink) Old 10-26-2017, 08:17 AM Thread Starter
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So, what does everyone think of the recipe... I'm getting low in salt for KH/GH+, so need to decide if i should mix and give it a go..

Can anything go wrong with the mixture above for livestock and if i replace the Calcium Sulphate Heptahydrate for Epsom salt without any additives, would I be good to go?

I will research the rest of the ingredients, but for the price of one tub of Salty Shrimp 100g, i can get over a kg!

Thanks,
Chris
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