# Tweaking James' RO remineralisation formula?



## JMorgan (1 Aug 2016)

I received a great deal of help here a while back and have been getting along quite nicely with using my tap water at about 10 to 20%. However the problem I have is that I have an RO reservoir of about 100 litres with an automatic cut off when its full. That means I have to chuck out 10 to 20 litres before I can add tap which is wasteful. Also, probably because I'm a bit of a control freak but also because the whole reason I have an RO unit is because the nitrates in my tap water are not just high but incredibly variable (30 to 60+ ppm). Yes I know the limit should be 50ppm but I'm not about to go head to head with Yorkshire water with an amateur test kit result they'll laugh at.

Anyway the point isn't that the nitrates are high, but that they vary massively and I want consistency and to eliminate a potential problem. I'm trying to revive dim memories (35 years ago!!) of an A level chemistry exam I just about scraped through, reading threads and generally educating myself.

That all said James' remineralisation formula aims for a GH of 5 and a KH of 1. The KH being deliberately very low because some plants thrive on it. I'm not sure I really need it that low and I'm (maybe unnecessarily?) a bit worried that I may not be experienced enough properly manage things if it goes wrong. 

(Italics pasted from James' web site)

_0.4g Calcium Chloride Dihydrate
2.0g Calcium Sulphate Dihydrate
2.0g Magnesium Sulphate Heptahydrate
0.7g Potassium Carbonate
per 25 litres Water_

So if I were instead to aim for a KH of 2 how would I alter the Potassium Carbonate amount? Is it as simple as just doubling it as its the only source of Carbonate in the mix? 

_1.5g NaHCO3 in 25 litres of water = 2 dKH
1.8g KHCO3 in 25 litres of water = 2 dKH
1.2g K2CO3 in 25 litres of water = 2 dKH_

In other words why isn't it 1.4g Potassium Carbonate (K2CO3)  = 2 dKH 
I'm quite happy to just make up the formula and trust that James knows what he's about, but I'd prefer to understand . . . 


Thanks in advance and thanks to James for all the valuable info


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## dw1305 (1 Aug 2016)

Hi all,





JMorgan said:


> Yes I know the limit should be 50ppm but I'm not about to go head to head with Yorkshire water with an amateur test kit result they'll laugh at.


Yorkshire Water can't lie about the level of NO3 in the water they supply to you. You should be able to get figures (min. , max and mean) for 2015 for your post-code and you can see if the water supply to your house has breached the EU (50ppm NO3) limit.  

Things have got better in recent years, but breaches still occur <"Quest to reduce...">. 





JMorgan said:


> In other words why isn't it 1.4g Potassium Carbonate (K2CO3) = 2 dKH


 The problem is dKH is worked out in a really strange way. The best explanation is probably still in <"The Krib:Water Hardness">.

You need to start from 1 dGH is defined as 10 ppm (mgl-1)  CaO, this has nothing to do with dKH (we don't have any CO3), but it means that 1dGH is equivalent to 17.86 ppm CaCO3, and that is also defined as 1dKH.

The CO3 portion of CaCO3 works out at 10.72 ppm CO3 (= 1 dKH), and each carbonate ion (CO3--) forms two bicarbonate ions (HCO3-) and 1dKH = 21.8 ppm HCO3.

You can then use the 10.72 ppm CO3-- and 21.8 ppm HCO3- to work out how much of any carbonate you need to add to raise the water by 1dKH for any given volume of water.

Potassium carbonate has the formula K2CO3. You need to work out the proportion of CO3 in K2CO3, to do this we need to know the RAM of K= 39 (2*39 = 78), C=12 and O = 16 (3*16 = 48), so the RMM of K2CO3 is 78 + 12 + 48 = 138 and the proportion of CO3 is 60/138 = 43.5%.

I'll use 100 litres as my volume (because it makes the calculation easier). 
1072 mg = 1.07g of CO3-- in 100 litres (or 2.18g of HCO3-) raises 1dKH. 

Adding 1g of K2CO3 adds 0.43g of CO3-- and adding 2.46g of K2CO3 adds 1.07g of CO3-- (and raises the dKH by 1 dKH) and 4.92g of K2CO3 raises dKH by 2dKH.

James uses 25 litres in his example, so we need to divide 4.92/4 to give his figure of: 

To raise 2dKH using K2CO3 *<"1.2g in 25 litre"*>.

cheers Darrel


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## JMorgan (1 Aug 2016)

Fantastic Darrel - I really appreciate you taking the time to explain all that.

Thank you!

Thanks also for the link to the Yorkshire Water page on the nitrate plant. I've actually visited the nature reserve but had no idea that plant did that! I will follow up to see what the figures are in any case.

I was talking to the owner of Ferrybridge aquatics a few days ago and he was describing how normal it was for species like neon tetras to spawn in people's community tanks 20 -30 years ago. It appears this intensive nitrate use is at least part of the explanation.


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## JMorgan (2 Aug 2016)

Just to check a few other things:
1) Can I mix up the ingredients in the correct proportions (multiples of James' formula) and store them together without problems?
2) if yes, would it be a good idea to add some food grade silica bags to the container to soak up some moisture? 
3) Given its now all in the right proportions can I revert to just using my TDS meter and aiming for around 120 ppm TDS or is this too simplistic?

The reason the last question is important to me is that I have seven tanks now, three of which need daily water changes because I'm growing out a load of fry - many more having survived than I expected! - so I may only use 60 litres of the 100 litre reservoir. Then it gets filled up over night and I need to add more minerals.   I got pretty good at chucking out water and adding tap to get back to between 100 and 120 ppm and I need to be able to do something similar with the DIY remineralising mix, but without wasting water . . .

My third question might be better phrased, "With all these "ingredients" being known quantities, including a starting point of 0ppm RO water, is it possible to calculate GH and KH (or a rough but still useful approximation of both) just from the TDS reading? 

Thanks again


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## dw1305 (3 Aug 2016)

Hi all,





JMorgan said:


> _0.4g Calcium Chloride Dihydrate
> 2.0g Calcium Sulphate Dihydrate
> 2.0g Magnesium Sulphate Heptahydrate
> 0.7g Potassium Carbonate
> per 25 litres Water_





JMorgan said:


> 1) Can I mix up the ingredients in the correct proportions (multiples of James' formula) and store them together without problems?
> 2) if yes, would it be a good idea to add some food grade silica bags to the container to soak up some moisture?


You can mix them together, but you would need to add a desiccant  because both the K2CO3 & CaCl2.2H2O will pick up further moisture from the atmosphere, they are <"deliquescent">. It would be easier to mix them into a stock solution and then dose that. 


JMorgan said:


> 3) Given its now all in the right proportions can I revert to just using my TDS meter and aiming for around 120 ppm TDS or is this too simplistic?


That would be fine. It would also get around the problem with dry salts, you just add enough of your dGH/dKH stock solution to get to 120ppm TDS (~185 microS conductivity).


JMorgan said:


> My third question might be better phrased, "With all these "ingredients" being known quantities, including a starting point of 0ppm RO water, is it possible to calculate GH and KH (or a rough but still useful approximation of both) just from the TDS reading?


Yes, you just need to use the formula from earlier in the post for dKH, the dGH formula is in the <"Krib post">. Make up a solution adding 2dGH and 2dKH in a known volume of RO (10 litres)  and just measure the ppm TDS or conductivity.

TDS meters really measure conductivity and use a conversion factor usually 1 microS = 0.62 ppm TDS).

cheers Darrel


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## JMorgan (3 Aug 2016)

Thank you so much Darrel - your stock solution suggestion is so much more practical than trying to keep the mixture dry!

Again I really appreciate you sharing your knowledge and understanding so generously.


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## JMorgan (8 Aug 2016)

Just a quick update having finally found the time to put this into practice. I made up a table with amounts of salts for 100 litres and 1000 litres, then got 1 litre of RODI water and weighed out the amounts for 1000 litres and put them in the litre of water. So now in theory I had a solution where 1ml of my remineralising solution should do 1 litre of RO water.

Anyone doing this should make sure they have a container that's properly water tight as you're going to want to shake it like hell before measuring out the volume you want to add. In only one litre of water the salts (for 1000 litre amounts) don't stay in solution, the best you can hope for is that having been shaken vigorously they are evenly in suspension. If i'd had a handy five or ten litre container, I'd probably have used that, but now I'm glad I didn't because it actually works very well, after a damn good shake! 

I added the required 100ml to my (approx) 100 litres of RODI (0 ppm on my TDS meter) and after running a big air stone in it to mix things up for about an hour the TDS was exactly 100ppm on my meter. 

So I reckon I spent less than £20 including postage on 1kg bags of the chemicals to end up with what seems to be several years supply of remineralising agents so I'm a very happy camper!

In preparing to do this I gave my reservoir a good clean out and was pretty disturbed to find quite a lot of reddish brown muck at the bottom of the barrel, which I assume is an accumulation of something not dissolving that was in Equilibrium. I can't think where else it can have come from - so hopefully this approach will avoid that problem too.

I'll try to figure out uploading my table in case its helpful to other folks here.

thanks again Darrel


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## Manuel Arias (19 Aug 2016)

JMorgan said:


> Anyone doing this should make sure they have a container that's properly water tight as you're going to want to shake it like hell before measuring out the volume you want to add. In only one litre of water the salts (for 1000 litre amounts) don't stay in solution, the best you can hope for is that having been shaken vigorously they are evenly in suspension. If i'd had a handy five or ten litre container, I'd probably have used that, but now I'm glad I didn't because it actually works very well, after a damn good shake!



Hi JMorgan,

You can make the solution easier to make if you do two things:

a) Dissolve each component separately in RO water, to avoid common ion effect, which makes harder to dissolve some salts.
b) By heating the water instead of doing it in cold water.

Both things together probably will significantly reduce the shaking needs. 

I never tried for aquariums, but in lab is common practice to prepare stock solutions of salts.

Cheers,
Manuel


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