Cloudy water in my new/used tank and starting to smell... Help

[Keelynnsreef]

I picked up a 185 gal tank with water,sand,live rock, eel,fish last week. I did not know I should have rinsed the sand after the move. They had put the sand in a big trash can and we moved sand with water to my house and they just put the sand and water back in the tank. I have done a 35% water change and the levels are still high. I am going to do a 50% today and was thinking I should either rinse the sand now or replace it all together. What should I do? I put clarifier in it and no help.

Can I put some live aggregate on top of the sand so the eel won't kick up as much sand. Or will this hurt the eel?

The water is still cloudy and starting to smell. Give me some suggestions I don't want to loose my fish. When I seen it set up at the other persons home the water was clear.