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Re: TDS vs. ppm

Bailin writes:

> With the recent talk about the Hanna TDS meters, I went and got one also.  
>  was very surprised that my water was over 500 tds, but only 76 ppm GH.  So 
>  what number do you actually use for breeding?  What's funny is that my RO 
>  water is also fairly high in TDS but not in ppm.  Confused to say the 
>    Any ideas?
Ro water isn't all that pure.  You may have a lot of sodium chloride getting 
through.  You membrane may also be old and due for replacement.  Many RO 
units have an optional DI second stage available for them.  Sounds like you 
may need one.  More and more folks are using Conductivity as the standard for 
breeding conditions.  This is a function of Total Dissolved Solids, or 
perhaps more appropriately, Total dissolved Ionic Charges, though I've never 
actually seen it refered to in that fashion.  Your TDS is probably a little 
higher than you want.

Bob Dixon

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