# What does it mean - ppm relayed



## nayr88 (26 Jan 2015)

Hi guys just wanted to understand this a little better

If my tap water has a reading of 600ppm as far as I'm aware it has 600 parts per million, could someone explain this a little further.

What are the 'parts' and a million is what ? Sorry if it's been gone over but I kept getting an error message when using the search button.

Cheers guys,


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## Jose (26 Jan 2015)

1 ppm =1 part (mass) of something (e.g NO3) for every 1 000 000 parts (mass) of water. So 1 mg of NO3 for every 1 000 000 mg of Water. 1 000 000 mg of water = 1000 g of water =1kg of water = 1 litre of water (because density of water is 1kg/l).
So 1ppm = 1mg of NO3 (or whatever molecule) in 1 L of water.

1ppm = 1g/L. This is really what you might need to know.

Someone else can get into conductivity ppms more in depth. So what does 600 ppm conductivity mean? Because there are many molecules adding up to the conductivity (mainly water hardness I suppose.). I suppose they measured different hardnesses (ppms of CaCO3 maybe?)and their conductivity and put the relationship into our conductivity meters.


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## dw1305 (26 Jan 2015)

Hi all,


nayr88 said:


> If my tap water has a reading of 600ppm as far as I'm aware it has 600 parts per million, could someone explain this a little further.


PPM is just a way of describing relatively dilute solutions.

Jose is right, 1mg per litre is 1 ppm and 1g per litre is 1000 ppm. You could present the same value as percentages or decimals, but they are more difficult to interpret.

If you use scientific notation I think it becomes easier. Percentages are parts per 100 (10^2), but we can have parts per thousand (10^3), parts per million (10^6), or parts per billion (10^9).

A lot of our students struggle with this, so I give the students a spreadsheet with a periodic table, numbers expressed as  powers of 10 from 10^-9 to 10^9, and some examples, and formulae, that allows them to convert from ppm to mols, and from ppm to grams for any dilution of a stock solution 

If you are talking about ppm "TDS"?, that is actually a measure of conductivity, where all the ions in solution are linearly related to electrical conductivity, expressed as ppm "total dissolved solids" (conductivity multiplied by a conversion factor, usually 0.64).

If we assume there really are 600 parts per million of all the ions in solution, that is 600 in 1,000,000 (10^6), knocking 2 noughts off either side, gives us 6 parts in 10,000 or 0.6g of salts in 1 litre (1000g) . 

TDS is a measure of all the ions, but we could use analytical techniques like "atomic absorption spectrophotometry", "mass spectrometry" etc. to get a value for an individual element.

cheers Darrel


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## ourmanflint (26 Jan 2015)

Jose said:


> 1 ppm =1 part (mass) of something (e.g NO3) for every 1 000 000 parts (mass) of water. So 1 mg of NO3 for every 1 000 000 mg of Water. 1 000 000 mg of water = 1000 g of water =1kg of water = 1 litre of water (because density of water is 1kg/l).
> So 1ppm = 1mg of NO3 (or whatever molecule) in 1 L of water.
> 
> 1ppm = 1g/L. This is really what you might need to know.
> ...


Jose 

I think you mean 1ppm = 1mg/l or 0.001g/l 

Rod


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## nayr88 (26 Jan 2015)

Thanks guys 

Darrel that's makes more sense. Thanks for the breakdown.
This leads me into my next question. 

If I have 1 litre of water, we will say that's 0.6g or salts....now I'm going to hazard a guess that it varies a fair amount but what exactly are the salts? 
Would I be right is saying there are some good salts in there and some non useful ones(in terms of plants) 

Thanks in advance, I've never looked past de chlorinating water, adding ferts and growing plants, it's interesting to understanding water a bit more, not just for aquarium keeping but also for plant growing in general


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## ian_m (26 Jan 2015)

Have play with this.

Set the following:

Tank size  1litre,
"DIY"
KNO3 is a good start
calculating for the results of my dose.
Select gr and enter your amount
http://calc.petalphile.com/

So your 0.6gr of KNO3 in 1litre of water will give 411ppm (value down bottom right). Other ppm values are for NO3 etc.


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## Jose (26 Jan 2015)

ourmanflint said:


> Jose
> I think you mean 1ppm = 1mg/l or 0.001g/l
> Rod


exactly sorry for that. Thanks Rod.


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## dw1305 (26 Jan 2015)

Hi all,





nayr88 said:


> If I have 1 litre of water, we will say that's 0.6g or salts....now I'm going to hazard a guess that it varies a fair amount but what exactly are the salts?Would I be right is saying there are some good salts in there and some non useful ones(in terms of plants)


 Yes, if you have hard water you could assume that a lot of the dissolved salts will be Ca++ and 2HCO3-. You should be able to get a break-down from your water supplier for your tap water. 

This link has the workings for a couple of water supplies <"What can a newbie learn from a local water quality report?">.





ian_m said:


> Have play with this.
> 
> Set the following:
> 
> ...


 I like this one, it has a lot of compounds listed, so saves a bit of  time finding the RMM of FeDTPA etc.

cheers Darrel


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