TDS question

[jvannis]

Doing some research on a RO/ DI unit and started reading about TDS. I may be reading this wrong but it seams like all the post I have read about TDS, you want 0ppm. I found this website that seems to say fish need a certain level of TDS
This is from http://www.tdsmeter.com/abouttds_aquaculture.html
"level of 400ppm or less is recommended for most freshwater fish although many softwater fish demand a significantly lower level. Conversely, saltwater fish require a very high level of anywhere from 5000 to 50,000 ppm. Total Dissolved Solids are also important for proper osmotic regulation, which is the relationship of water versus dissolved solids in the cells and the external environment. The greater the amount of solids in the water versus the solids in the tissue of the fish will result in a fluid loss via the gills. ³"
Just hoping someone can set me straight on this topic.
Thanks

 

[gillyweed]

Salt is a dissolved solid as well
RO/DI water should have no dissolved solids, IE pure water. Once you have that then you can add your salt mix (heating and circulating the water as well, etc etc) to raise the TDS to a proper level for saltwater fish.
by doing this (using RO/DI water) you are ensuring the only TDS in your system are the ones you want; and there are no "extras"

but that is just my guess

 

[1journeyman]

Originally Posted by Gillyweed
.... RO/DI water should have no dissolved solids,.......
Exactly right. 0 TDS is referring to RO/DI water.