[malcnunn]

Hi
I am a hobbyist studying marine biology and have been aquaculturing hard corals for a number of years . I have recently had an ICP test done on our water and after chatting with other hobbyists it seems many if not all manufactured salts (that we mix with RoDi) have uimpurities (some have high Zn etc etc).
My question is this , would anyone like to give me advice or help me create a pure salt mix ? Is it even possible due to the amount of trace elements required ?
Many thanks in advance 

malcolm
 

[Dan]

pure salt mix

What do you mean by this? For a chemist, the terms pure and mixture are mutually exclusive.

[billnotgatez]

@malcnunn
I assume the reason why you want pure Sodium chloride is to be able to control the chemical composition of the water you use during an experiment
But
How does the substitute sea water you make compare to actual sea water?

Detailed composition of seawater
http://www.seafriends.org.nz/oceano/seawater.htm#composition

Could you explain your term

with RoDi

So that other members on this forum might follow the discussion.

I assume that

ICP test

is
Inductively coupled plasma mass spectrometry
http://en.wikipedia.org/wiki/Inductively_coupled_plasma_mass_spectrometry

[malcnunn]

thanks for the replies , I will try to explain best I can and apologies I am not a chemist by any means
I currently use reverse osmosis water that has been ran through de ionisation resin so that I end up with water at 0 tds (total dissolved solids).
I then mix this with synthetic sea salts to make sea water .Different manufacturers of these synthetic salts (I assume through manufacturing or from evaporation of brine etc) have varying degrees of excess or insufficient amounts of trace elements .
After a period of time this causes issues in our coral tanks from doing water changes (the excess elements build up and visa versa) and we have varying issues that stem from this .
I was wondering if it would be possible to start with pure NaCl and add each of the other elements seperately to make a synthetic salt that matched very closely to the composition of natural sea water . Because of the low amounts of elements needed I thought maybe it possible to make up some form of liquid for all but the major components (NaCl, Ca ,Mg etc ).
Also , yes, ICP is Inductive testing (we send our samples to Germany each month for this .. If anyone here in the UK does this I would be happy to know
Thanks again for reading .

Malc

[Arkcon]

I can follow the gist of what you say fine, but yo make some assumptions that aren't really true, or apt, and that gets in the way of a useful answer.  But lets try anyway.

thanks for the replies , I will try to explain best I can and apologies I am not a chemist by any means
I currently use reverse osmosis water that has been ran through de ionisation resin so that I end up with water at 0 tds (total dissolved solids).

Se, this isn't necessarily true or apt.  There will always be some contamination, even from leaching out of containers that you use for storage or transfer.  So maybe its not as important, but still, getting definitions correct at the start keeps us from getting into trouble later.

I then mix this with synthetic sea salts to make sea water .Different manufacturers of these synthetic salts (I assume through manufacturing or from evaporation of brine etc) have varying degrees of excess or insufficient amounts of trace elements .

I worked briefly for the phycology lab when I first started at university and what he did for algae culturing was to collect ocean water, filter it, and store it for later use.  He said there was really no other way to really get the trace elements correct for routine classroom culturing tasks.  It was autoclaved to kill spores before use.  Drying it would present some problem of homogeneity, but I guess manufacturer's have some sort of workaround.  Trying to get a growth medium perfect by mixing all components can be a challenge, so we only do that when necessary.

After a period of time this causes issues in our coral tanks from doing water changes (the excess elements build up and visa versa) and we have varying issues that stem from this .

Hmmm... this seems like something that might happen anyway.  The corals will deplete any media, natural or otherwise, as they sequester elements within themselves.  So I don't see how your plan, is a workaround.  Maybe you just need a bigger tank  so these changes aren't as severe?  Or gradually change the water with a fresh preparation?

I was wondering if it would be possible to start with pure NaCl and add each of the other elements seperately to make a synthetic salt that matched very closely to the composition of natural sea water . Because of the low amounts of elements needed I thought maybe it possible to make up some form of liquid for all but the major components (NaCl, Ca ,Mg etc ).

Yes, people do prepare those.  http://en.wikipedia.org/wiki/Artificial_seawater  There are international standards that define the limits, and a number of specific recipes.

Also , yes, ICP is Inductive testing (we send our samples to Germany each month for this .. If anyone here in the UK does this I would be happy to know
Thanks again for reading

There are many sources.  A good one could be the vendor who sells you your salts.  They may take your used salts, determine what's depleted/built up, and suggest how you can adjust your media.  They get a satisfied customer, they get to sell you new salts, and they get to learn something.  That could be enough of a win-win-win for them to swallow the cost of the test.