Auto topoff question

I have a stupid question about auto top offs. The one I am setting up will have a container with water next to my sump under the tank. Now, should I fill the container with saltwater or freshwater. I'm asking this because I heard that as water evaporates the salinity level rises, so you should top-off with freshwater. Is this true? Thanks.

 

Yes your top off water due to water evaporation should be freshwater (RO/DI)

 

Thanks for the answer! I'll make sure to use freshwater!

 

Do you have any pictures? I was thinking of making one with a toilet float valve.

 

Funny as Ive said in other posts i'm a fan of DIY projects due to lack of money and I was thinking of doing a topoff with toilet float valve myself last night, i have heard they work well.

 

My brother-in-law put one in his coy pond. It works great. I'm not sure how much the salt will muck it up.

 

Not yet, but I can post some when it's finished if you want.