The soil sample should be of the pond basin and surrounding areas....several small dirt clods dried then mixed thoroughly to gate the general PH and fertility of your soils.

If you go the Alum route using Jar tests to determine an application rate, keep in mind this gives you the minimum amount required...I always double that before getting good results.

Again, buffer the alum with 50% by weight of HYDRATED Lime....NOT AG lime...there is a huge difference and could mean the difference between helping and killing your fish.

I would also suggest you fish your pond or set out some jug lines using chicken livers as bait for bullheads and soured corn dough balls for any common carp, just to remove them or know that they are there. Both fish root around in the sediments and cloud the water badly.