If you have liverock, which I highly recommend fresh water will destroy it, now that I do auto water change in my large system I do not have much water coming out all at once. I could go large on my small system and donate 30 gallons if that would help. There is not much bacteria in the water column so fresh made up salt will work similar to recycled tank water. I am 8n 90630 and am doing a water change on my smaller system later today.