Ammonia spikes are dangerous and a terrible event that can lead to the death of koi. I know from personal experience that when putting a new pond together everything seems to be right on for a couple weeks. Then when you add your fish and begin to feed them regularly, you may not have much of the ugly green water that defeats the purpose of buying beautiful koi. Many suggestions are out there for combating the algae when it appears. The most popular that I know of are UV lights, and chemicals. I happen to have two very high stregth UV lights. And when I set up the system I was not really using them because the water was so clear. When I noticed the green shadow taking root in my pond I turned on the lights. Also, you should know that when I set up the new pond I had left them off so that the beneficial bacteria could take root. So I turned on the lights after about a month. I couldn't help but notice the spike in the day following this. The ammonia had appeared in extremely high over night. So my suspicion was that the lights may have affected the algae and the beneficial bacteria because when I turned them off the ammonia was still climbing. After a healthy water changes, ammonia binder, and more beneficial bacteria and leaving the UV off I noticed things got back to normal. So I turned the light back on as an experiment to see if it was indeed the light causing the problem. In essence it was. See what appears to be the cause is the death of all that algae leaving ammonia and suffocating the fish because the lack of oxygen etc. Then I had to completely redo every step over to get the pond back on track. This can be a stressful event not only for your koi but for you as well. After speaking with several people and reading on the subject I felt that I could solve the problem. What I found was that there are several ways. One is to set your UV lights on a timer and run them for a short period so that your system is not shocked. After all you do not want to shock the system. You can also do water changes while this is going on. Finally add a very small amount of Algaway 5.4. And I do mean a small amount. This will help to clear the water when you want to clear the cloud out. Then your water will be very clear. Make sure that you maintain your water changes regularly and increase the light timer for your UV until you can leave it on. This process can take a while but It is worth it. Enjoy your Koi and Happy Keeping!