For what it's worth I do a 20 percent water change in my 250 gallon systems as frequent as every other day to once a week depending on the species and tank load. I could probably get by with less. I once had 75 lbs. of yellow perch in 150 gallons of water and did a once a day water change as a solid back mass of fish made me nervous!
I also flush out around 2 to 4 gallons in the center drain and around it twice a day by opening a knife gate valve on the external stand pipe. Let me tell you that is some foul smelling stuff!
My make up water is premixed with salt, heated, and the iron precipitate filtered out. I've never seen a substantial rise in salinity from evaporation and even if I did it wouldn't be an issue as long as it's gradual.
I have grown both tilapia and bluegills in an outside system in the summer with no salt added as the waste water was used on a nearby raised garden. No health issues whatsoever. The PHD down the road that raises hybrid striped bass for the Chicago gourmet market doesn't use salt either.
That said if given the choice I prefer to add salt.
Last edited by Cecil Baird1; 09/16/15 10:40 PM.
