to make a long story short. i have a 1.5 acre pond. i had a bad duckweed problem. i used reward and killed all the duck weed. i had a fish die off before i sprayed. my water is now a oily black slime color. have I had a die off or am I close. is the black color due to the decomposing duckweed. i have only seen about 10% of the fish I put in floating. would they all be floating or do some sink. What do I do now, thanks