if plants and fish are fine... it should be fine.
Phosphate release from a freshly submerged soil should slow with time as the soil "settles down" in the coming months. After that, fishfood will start adding phosphate to the water. Much of this phosphate will precipitate to form various calcium phosphates and iron phosphates. These precipitates will collect in the soil (as plant nutrients!) and biofilter.The phosphate in my soil seems to get into the water easily. I guess it is still coming out of the soil in relatively large amounts.