The problem that actually happened and were killing the Koi fish was that the pipes that was filtering the water into the pond were lead pipes. Soon enough, the fish started getting lead poising, causing them to die. My house was built in 2000, so that was quite a while ago. We had always wanted to get Koi fish but didn't get around to that until 6 months ago. Having the pond be built in 2000, the contractors thought that we weren't going to house any animals in the pond, so they used the most durable pipe out there. At the beginning of each week, we started out with 15 fish. With the first experiment, trying out a different diet, there were a total of 2 fish at the end, and making that an average of 10 fish per day. The second experiment, adding nutrients to the water, there was a total of 7 fish in the end with a 10.29 average of fish per day. So yes, the nutrients DID help but there was still over 50% in reduction of Koi fish that week. So, I enlisted my handy mechanical engineer father and we investigated the pond. We didn't know that the pipes were lead at first but, did notice that they were really old and rusty. We then made a trip to The Home Depot and bought new PVC pipes and re-piped the whole pond. At the end of that week, we were with 14 fish, with an average of 14.43 fish a day! We did a little more research and found out that Koi fish are susceptible to some of the same diseases humans are! We are still unsure why one of the fish did die, but we are ruling that as natural causes. This experiment could've been disrupted because we did use the left over fish from the previous experiments and not starting with a fresh batch of 15. Also, some of the fish were older in age and could've had some other diseases which caused them to die. This experiment could be applied to all fish owners, make sure your pipes are not lead!