# What that means xH2O ?



## crazyhorse (8 Aug 2016)

Hi all!
I can buy NaH2PO4 in some chemical store near by. When I asked about it they said to me they have 
1. NaH2PO4 x2 H2O and
2. NaH2PO4 x12 H2O 
That confused me a little. Need help about how this chemical is calculated for dissolving Maybe some online calculator for this form of chemical
TY


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## rebel (8 Aug 2016)

All else being equal, Get number one. Is this for your tank? Best to get K2PO4.


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## ian_m (8 Aug 2016)

Are you sure you don't mean K2PO4 and KH2PO4 ? Na (sodium) has no place in fresh water aquariums.

This calculator supports both type of PO4.
http://yanc.rotalabutterfly.com/


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## dw1305 (8 Aug 2016)

Hi all, 





crazyhorse said:


> 1. NaH2PO4 x2 H2O
> and
> 2. NaH2PO4 x12 H2O


It would be either the dihydrate (2H2O) - NaH2PO4.2H2O, or the monohydrate NaH2PO4.H2O. In use it will always be the dihydrate, because it is hygroscopic and will pick up moisture from the atmosphere. 





ian_m said:


> Are you sure you don't mean K2PO4 and KH2PO4 ? Na (sodium) has no place in fresh water aquariums.


I agree with "ian_m", and "rebel", that potassium hydrogen phosphate (or potassium dihydrogen phosphate) would be a better salt to use. I think the di-potassium salt will end up as K2HPO4.3H2O.





crazyhorse said:


> That confused me a little. Need help about how this chemical is calculated for dissolving Maybe some online calculator for this form of chemical


You need to add together the RAM of the constituent elements to get the RMM of the compound ("salt"), and then work out the percentage of the elements you are interested in, in this case (K and PO4). 

This process is automated in a dosing calculator, like the "rotalabutterfly" one linked. 

cheers Darrel


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## crazyhorse (8 Aug 2016)

Ok potassium hydrogen phosphate is my choice too then.
TY all for quick answers


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