Does your pond have a halocline? Or do the fish keep it stired up enough so the salt stays in suspension permanently?
When diving along the Mexican Yucatan coast and in the cenote's I often ran into a halocline. The heavier sea water would sink, and the lighter fresh water would be on top. An intermediate layer a few inches thick in the transition always a shimmery area where view of anything was distorted. Above was clear, below was clear, but at the halocline the water was really cool looking.
Having not been exposed to it, the average person might assume the two waters would mix immediately, but the do not. It takes some wave agitation or time for them to equalize and the heavier and lighter water to become one.
