# Swap from RO to tap & rain



## tam (24 Dec 2020)

I'm moving and logistically it would be easier to swap from remineralised RO to tap+rainwater, I think. 

I currently use RO remineralised with Salty Shrimp GH/KH to about 220 TDS.

The tap water report is:

311 mg/l (or parts per million)     :Calcium Carbonate
        124.4 mg/l (or parts per million)     :Calcium
        21.646 °C     egrees Clark
        31.1 °F     egrees French
        17.665 °dH     egrees German
        3.11 mmol/l     :Millimoles

What would you mix rain/tap proportions too?  Anything else I should keep in mind?


----------



## dw1305 (24 Dec 2020)

Hi all,


tam said:


> What would you mix rain/tap proportions too? Anything else I should keep in mind?


No, just re-mineralise it to the 220 ppm TDS  with the tap water. 

cheers Darrel


----------



## tam (24 Dec 2020)

That was might first thought, but the maths didn't seem to add up.

The Saltyshrimp says 300µS = 6gh, which I work out as 190TDS (dividing by 1.56) so my 220TDS should be about 7GH. I think the tap is about 315TDS, so if I dilute to 220 that's about 12.3GH... which is quite a bit harder.

Maybe I need to test the actual GH's involved.


----------



## dw1305 (24 Dec 2020)

Hi all,


tam said:


> The Saltyshrimp says 300µS = 6gh...
> 
> 
> tam said:
> ...


Yes that is right I think. It will be other salts  in the SaltyShrimp, ones that don't contribute to the dGH. The tap water ions will nearly all be Ca++ and HCO3-, which contributes equally to dGH and dKH.

cheers Darrel


----------

