Hi there My Hubby and I bought a property 9 months ago with a garden pond with 3 gold fish and 3 Koi. Pond about 6 foot by 3. We knew very little about fishkeeping. Everything was OK till this weekend. We had de-aglaed the pond a few months back and it had been fine. We were feeding them everyday and enjoying seeing them zipping around. On Saturday I cleared some plants that were choking the pond and stopping them from reaching the other end of the pond. My hubby de-algaed then put the pump on. Then A few hours later we noticed fish at the top of the pond and bubbly stuff at the surface of the water. Sadly 5 out of 6 of them died. We feel really sad and bad about it. I think we may have inadvertently killed them due to ammonia or lack of oxygen. We really don't know. However 1 has survived. He/she seems to be hiding from the world and isn't taking the food I have put out for him/her. Can anyone advise how we can take care of this little fellow. Is he feeling frightened and lonely?