Old Saltwater to culture Brineshrimp and Phyto and Rotifers

[themastr]

I live in an acreage and far away to always get salt. LOL
But my main worry is I can't dump any of the old saltwater in my septic tank it will kill and rust the pump and all the bacteria needed to work properly.
My tank volume setup is about 350 gallons going to be 450 Gallons. So every water change is a lot of old saltwater. I usually just put it in the yard somewhere but I was trying to not kill what little grass I have left. LOL
I will probably just buy IO and use that I was just hoping that I can reuse the old saltwater somehow instead of going to waste. I waste enough water using R/O for the whole tank. Good thing water is from a well and FREE minus the energy to run the pump.

If anyone else has experience I would love to hear from you.

thanks
erick