After research this is whats happens to the water.
There is lots of life in ocean water (plankton) that dies if the water is not oxygenated. So after 2 days you have lots and lots of dead items rotten in the water. You need to either let it set for a few weeks, then only use the clear water on top, or filter it, very very well, or kill it with chlorine, filter and dechlorinate.
Problem solved but seams like alot of work to me.