why are my fish dying

Question
Hello, I have had a pond for about ten years. We even moved and took our fish with us and lost one fish in the move.  All of my fish were very old and last summer we had a herring get alot of my fish.  The herring did alot of damage to the liner of the pond and we had to replace it. Ever since we replaced the liner we have been losing fish.  We also put in a bio filter which keeps the pond water clear.  We were told that we made our water to clean and the fish were dying do to lack of bacteria. We got that problem fixed but a few weeks ago it was very cold and I went to the pond only to find all fish dead.  We cleaned the filter and went and bought feeder gold fish just to reestablish the pond but they have since died for the most part.  The ones that have survived stay very close to the bottom and group around the pump box, they are not eating or swimming they just kind of float around.  I have added pond salt but now I am getting this hair like algea.  My fish seem very sick what can I do.

Answer
Hi Emory,
Thanx for your question.  Hair algae starts occurring about this time a year.  You can go to a store that specializes in ponds and buy a small package of barley straw and it will help control the hair algae.  All I can tell you is that it sounds like your fish have gone through shock.  It is true that you shouldn't clean the pond on a regular basis.  There are  bacteria that fish need to maintain the "slime" on them which protects them from disease.  Very clean water will "clean away" the slime.  There are products you can buy at the pond store that will help fish maintain their slime.  The heron may have introduce a disease into the pond from other fish it ate.  I hope this helps.
Tom