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Another question about mineral balance of RO/DI water

FrankR

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I'm "forced" to use RO/DI water for my water changes because my tap water has high NO3 (~40ppm) and I've already bought Seachem Equilibrium to remineralise it.
I've already read many threads about remineralising RO water, but I'm a bit lost. Frankly, the more threads I read, the more confused I am.
The GH in my tank is 15 dGH. If my maths is correct, to lower it to 9-10 dGH I'd have to add 3 g to 15 litres of RO/DI water (for a 50% WC). Please correct me if I'm wrong.
However, I've just realised that Equilibrium affects only the GH, not the KH. Does that mean that the KH will drop by half if I do 50% WC?

Cheers!
 

Hanuman

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and I've already bought Seachem Equilibrium to remineralise it.
That's a shame because you are paying big box for something that could cost you pennies by simply buying and using CaSo4 (Calcium Sulfate) and MgSO4 (Magnesium Sulfate). Additionally Seachem Equilibrium also contains K (Potassium) and Fe (iron) which might not be desirable since you are already adding K and Fe with your TNC Ferts. Your K will skyrocket with Seachem Equilibrium.
I've already read many threads about remineralising RO water, but I'm a bit lost. Frankly, the more threads I read, the more confused I am.
Will try to clear that up for you. What exactly is it that you can't figure out?
The GH in my tank is 15 dGH. If my maths is correct, to lower it to 9-10 dGH I'd have to add 3 g to 15 litres of RO/DI water (for a 50% WC).
No. When you remineralize you do so by remineralizing the WC volume, not the tank volume unless you are doing a 100% WC or that it's the first time filling up the tank. To bring your dGH to the desired target first do a 50% WC without adding any remineralizer. That should cut in half your dGH and bring it to ~7-8 dGH. It doesn't have to be precise. Subsequent WCs will have to be remineralized up to the dGH you want. So if you are adding 3g to 15L of RO that would equate to ~3dGH (for the WC volume). If you want want 9dGH you would need to add ~9.5gr of Seachem Equilibrium.
Screen Shot 2022-06-02 at 07.58.39.jpg

Seachem uses the meq/L unit, so 1 meq/l =~3dGH therefore 3meq/l =~9dGH

However, I've just realised that Equilibrium affects only the GH, not the KH. Does that mean that the KH will drop by half if I do 50% WC?
If using pure RO, yes KH will also be cut in half. If you don't have fish in there, then no big deal. If you do have fish/shrimps etc it might be wise to slowly decrease your KH.

To sum it up, I would suggest you get CaSo4 (Calcium Sulfate) and MgSO4 (Magnesium Sulfate). That way your K and Fe will remained untouched. Also you can use the IFC Calcualtor to figure out the weights. I've made a small simulation with 9dGH for you to give you a head-start. I kept the exact same Ca:Mg ratio used by Seachem Equilibrium.

1654132588397.png

1654133234445.png

1654133249319.png

Here is a price comparison so you know what you are wasting ;)
1654133560399.png
 
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FrankR

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Thank you for your help @Hanuman !

That's a shame because you are paying big box for something that could cost you pennies...
I know. I bought it after reading a bunch of posts and at the time it seemed like a good choice.

To bring your dGH to the desired target first do a 50% WC without adding any remineralizer. That should cut in half your dGH and bring it to ~7-8 dGH.
That makes sense. But I do have an Amano shrimp in the tank. I guess a 50% WC with pure RO/DI wouldn't be wise. So I'll decrease it slowly like you recommended.
To sum it up, I would suggest you get CaSo4 (Calcium Sulfate) and MgSO4 (Magnesium Sulfate). That way your K and Fe will remained untouched.
Will do that. And what can I use to keep the kH stable?
Also you can use the IFC Calcualtor to figure out the weights. I've made a small simulation with 9dGH for you to give you a head-start. I kept the exact same Ca:Mg ratio used by Seachem Equilibrium.

View attachment 189403
View attachment 189404
View attachment 189405
Here is a price comparison so you know what you are wasting ;)
View attachment 189406
I dowloaded the IFC Calculator but either it doesn't work properly on Mac, or I'm too thick to figure out how to use it.
Anyway, I noticed that you've entered 15 l tap water and 15 l RO water for the WC. That's 100% WC, as my tank is 30 l. Shouldn't it be 15 l RO water only?
Cheers!
 

Hanuman

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That makes sense. But I do have an Amano shrimp in the tank. I guess a 50% WC with pure RO/DI wouldn't be wise. So I'll decrease it slowly like you recommended.
dGH swing is not a big deal for fish/shrimps. It's the dKH that is.
Will do that. And what can I use to keep the kH stable?
There is nothing you need to do. dKH is not technically required so I wouldn't sweat about it. What is your TAP water dKH at?
I dowloaded the IFC Calculator but either it doesn't work properly on Mac, or I'm too thick to figure out how to use it.
I made sure the IFC calculator worked on both MAC and Windows. The problem could be that you are using an older version of Excel which could be the reason. Check the "Spoiler: Technical notes" in the OP see if that is the reason.
Anyway, I noticed that you've entered 15 l tap water and 15 l RO water for the WC. That's 100% WC, as my tank is 30 l. Shouldn't it be 15 l RO water only?
Apologies for that. It was just so that a warning would pop up in the first image else it would show something else but I grossly omitted it would impact dosing quantities. This said, I just realized something. Are you planning on using only RO each time you do a WCs or are you planning on doing 50%TAP +50%RO , meaning 7.5L TAP + 7.5L RO?
 
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FrankR

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Are you planning on using only RO each time you do a WCs or are you planning on doing 50%TAP +50%RO , meaning 7.5L TAP + 7.5L RO?
My tap water has 14dKH and 18 dGH (API drop test).
My tank water has 8dKH and 14dGH (API drop test).
So, at first I was thinking of doing a WC with RO/DI water only and remineralise it with Seachem Equilibrium. But I don't won't to use it now, as I don't want my K to skyrocket, like you said.
So, I guess it's best to do a 50%Tap+50%RO/DI WC for now. That would have minimum impact on the tank's KH (~1dKH), would lower the GH to 11-12dGH and add only 20 ppm of NO3, instead of the 40ppm NO3 my tap water has.
I guess I could do that for all WC from now on. The KH will eventually stay at 7dKH and the GH will drop to 9dGH, correct?
It would also be useful if you have your water report to see what the TAP water dGH, calcium and magnesium contents are.
Here's the tap water report
Water parameters.png
 

Hanuman

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So, at first I was thinking of doing a WC with RO/DI water only
Doing so, you will eventually end up with 0 TAP in the tank, which is ok as long as you remineralize accordingly.
So, I guess it's best to do a 50%Tap+50%RO/DI WC for now. That would have minimum impact on the tank's KH (~1dKH), would lower the GH to 11-12dGH and add only 20 ppm of NO3, instead of the 40ppm NO3 my tap water has
That would be wise. You could even start with a 80%TAP-20%RO etc if you feel you want to be safe and progressively increase RO proportions.
I guess I could do that for all WC from now on. The KH will eventually stay at 7dKH and the GH will drop to 9dGH, correct?
Yes, there or there about, depending if you have substrate that will affect you GH and KH.
Well up until your aqua soil depletes. You said that your tap water is at 14dKH and your tank water at 8dKH. This is telling me that your soil is buffering and it's bringing your KH down. Once the soil loses its buffering capacity, KH will start creeping up to baseline TAP water levels unless you increase the proportion of RO in your WC schedule. At current levels of dKH, your soil will get depleted pretty fast though.
Strictly looking at your water report and calculating the hardness, it tells me that your TAP water is at 18.7dGH and 16.7dKH so your test kit is telling you more-less the right thing. So by merely cutting your WC with 50%TAP+50%RO you will be cutting those values by half. You could then progressively do a 60%, 80% etc until 100%RO WC if you wish to completely cut dkH. You will then have to start remineralizing with Ca and Mg. However I would suggest using MgSo4 from now on even at 50%RO+50%TAP because Mg is on the low side already.

Hope this helps.
 
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FrankR

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Yes, there or there about, depending if you have substrate that will affect you GH and KH.
I have Tropica Aquarium Soil Powder. My tests show it does affect both KH and GH.
Strictly looking at your water report and calculating the hardness, it tells me that your TAP water is at 18.7dGH and 16.7dKH so your test kit is telling you more-less the right thing. So by merely cutting your WC with 50%TAP+50%RO you will be cutting those values by half. You could then progressively do a 60%, 80% etc until 100%RO WC if you wish to completely cut dkH. You will then have to start remineralizing with Ca and Mg. However I would suggest using MgSo4 from now on even at 50%RO+50%TAP because Mg is on the low side already.

Hope this helps.
Helps a lot!
Ideally, I'd like the KH to be 7-8 and the GH 9-10 dGH. I plan to add a Nerite snail. These values would be ok for both the snail and the Amano.

Thank you all for your advice!
 

FrankR

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To sum it up, I would suggest you get CaSo4 (Calcium Sulfate) and MgSO4 (Magnesium Sulfate).
One last question, before I order the salts. Does it matter if it's Calcium Sulphate (CaSo4) or Calcium Chloride (CaCl2)? Is one more soluble than the other?
 

X3NiTH

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If there was any reason to use Sulphate over Chloride then you can look at the analysis of tropical rainwater to find the that in ratio there is usually more sulphate present than chloride, these are the minimums.

Chemical composition of rain water and rain characteristics at Delhi

For means to maximums once rain has fallen geology then becomes the dominant factor for surface water makeup and it’s a very moveable feast.

Your tap water has roughly equal amounts of both sulphate and chloride present, using either one over the other will likely not matter in the long run at the mg/L you are targeting for.

Calcium Sulphate stores better than Calcium Chloride which absorbs water readily from the atmosphere if it is exposed to it (why it’s used as a desiccant) so you have better guarantees with sulphate that you are adding the same amount of calcium for the measured weight.

:)
 

FrankR

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CaCl2 (1345g/L) is way more soluble than CaSO4 (2.4g/L), however considering your tap water is bringing the Calcium you probably will not even need Calcium unless you decide to go 100% RO with your WCs. But even then lots of people use CaSO4, me included. I prefer to add sulfates than chloride, for some unscientific reason 😗.

If there was any reason to use Sulphate over Chloride then you can look at the analysis of tropical rainwater to find the that in ratio there is usually more sulphate present than chloride, these are the minimums.

Chemical composition of rain water and rain characteristics at Delhi

For means to maximums once rain has fallen geology then becomes the dominant factor for surface water makeup and it’s a very moveable feast.

Your tap water has roughly equal amounts of both sulphate and chloride present, using either one over the other will likely not matter in the long run at the mg/L you are targeting for.

Calcium Sulphate stores better than Calcium Chloride which absorbs water readily from the atmosphere if it is exposed to it (why it’s used as a desiccant) so you have better guarantees with sulphate that you are adding the same amount of calcium for the measured weight.

:)

Hmmm... that's interesting! Because the rain water in Amazon has different amounts of Sulphate and Chloride than Delhi. For example, in Boa Vista Chloride is about 8 times higher than Sulphate. I guess the ratio between the two depends on the area where the rain water is collected and subsequently won't matter which one I use. But the fact that Sulphite stores better than Chloride is an advantage. So Calcium Sulphate it is then.
Thank you for your advice!
 

X3NiTH

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The ratio of Chloride to Sulphate in seawater is about 10 : 1 so rain from evaporating seas should contain roughly the same ratio, increased sulphate content over Delhi would likely come mainly from Anthropogenic activity, (clearing land, burning coal, etc).

:)
 

dw1305

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Hi all,
I'm "forced" to use RO/DI water for my water changes because my tap water has high NO3 (~40ppm
You can still use the tap water, <"plants are very efficient"> at using nitrate (NO3-) and in planted tanks levels will go down over time, rather than up.
My tap water has 14dKH and 18 dGH (API drop test).
Here's the tap water report
You will have ~17 or 18 dGH and 17 or 18 dKH, both are derived from the 299 mg/L CaCO3.
......... 1dKH is equivalent to 17.85 milligrams of calcium carbonate per litre of water......... 1 dGH is defined as 10 milligrams (mg) of calcium oxide (CaO) per litre of water, CaO has the RMM of Ca(40) + O(16) = 56. and 40/56 = 0.714. Therefore 7.14mg of Ca per litre of water is equivalent to 1dGH,......... .
Basically your water comes from a chalk aquifer and is fully saturated with calcium (Ca++) and (bi)carbonate ((2)HCO3-) ions. You don't need to remineralise your RO water, you just need to add a little bit of tap water (10% tap is plenty) to supply some calcium. You will add magnesium (Mg) with your fertiliser addition, because your water only contains a <"trace for geological reasons">.

cheers Darrel
 

FrankR

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You can still use the tap water, <"plants are very efficient"> at using nitrate (NO3-) and in planted tanks levels will go down over time, rather than up.
About that. I asked on another thread but no one replied. Perhaps you could clarify it for me.
I've read that most aquatic plants prefer to use ammonia, rather than nitrates, to live and grow. I quote:
Diana Walstad in her book Ecology of the Planted Aquarium, says that aquatic plants take up ammonium more quickly. In the case of Dwarf Water lettuce, “the turn over” time was found to be 4 hours, while nitrates turnover required a full 20 hours. Therefore, the fact that most terrestrial plants grow better with nitrates does not change the fact that for aquatic plants, nitrates are not their first choice.
Does that mean that if there's the usual production of ammonia (i.e. fish waste, fish food, etc.) in the tank and very low nitrates (0-5 ppm), plants still grow normally?
Basically your water comes from a chalk aquifer and is fully saturated with calcium (Ca++) and (bi)carbonate ((2)HCO3-) ions. You don't need to remineralise your RO water, you just need to add a little bit of tap water (10% tap is plenty) to supply some calcium. You will add magnesium (Mg) with your fertiliser addition, because your water only contains a <"trace for geological reasons">.

cheers Darrel
Oh, it's that easy! Thank you Darrel!
 

dw1305

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Hi all,
read that most aquatic plants prefer to use ammonia, rather than nitrates, to live and grow. ...........Does that mean that if there's the usual production of ammonia (i.e. fish waste, fish food, etc.) in the tank and very low nitrates (0-5 ppm), plants still grow
Yes, I wouldn't worry too much what form fixed nitrogen takes, basically plants take up all forms.

We are interested in ammonia (NH3) and nitrite (NO2-) because they are toxic to livestock, while nitrate (NO3-) isn't.

If you are a plant, it doesn't matter, <"they are all "food">.

Cheers Darrel
 
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