I have a pond of 12 small assorted domestic Koi. Do I need to drain the water from the tuna first? Do I just dump the entire thing in the pond or give them little bits at a time? I was thinking of mixing it with some filtered water to make it more mushy and mash it up as much as possible. I usually feed them as much koi pellets as they can eat in 5 minutes. Should I use canned tuna or should I buy fresh raw tuna from the fish market?