Fish keep dying no matter what we do!

Question
QUESTION: We had a small pond (around 300 gallons) for about 20 years with a couple of goldfish in it and a few water plants, a filter, and everything was fine. We never had any problems. We recently expanded the pond (now 700 gallons) and we started having problems. People came and expanded the pond, put a plastic-like liner and a bigger water fall. They said I did not need a filter, and I was very uneasy about this but they said the plants will be a natural filter. Well obviously they are wrong. Only maybe 2 months later my fish were all lying on the bottom of the pond huddled together with closed gills. I went to the local pond store and they gave me instructions to test the water for ammonia, pH, nitrites/nitrates, and things were a little off. I bought a filter because the water was so dirty. I tried changing the water and adding proper chlorinating chemicals. We tried everything. But the fish (within 2 weeks) are dying one by one. We had 4 big gold fish that we had for about 6 years; they all died. And we also bought 6 new baby gold fish/koi. And currently all but one of those are dead. So 9 out of 10 fish have died within 2 weeks. The last one is looking like its on its way out. We tried everything; medicine for ammonia poisoning, adding filters. We are very careful that everything is done carefully with the chemicals we put in the water so stabilize it. They swim near the top of the water or hide in plants, and swim all backwards and weird, sometimes even gasping for air almost when they are about to die (will not eat either). What can the problem be! They keep dying and we have no idea why! We've tried everything. Please help!

ANSWER: Hello Melina!
So sorry to hear about your fish!
These types of problems can be hard to diagnose, especially from a distance, but here are a few areas that can turn into problems real quick if installation is not done correctly:
1) What type of liner was used? Sometimes unscrupulous installers use roofing rubber instead of fish safe pond liner (roofing rubber is cheaper). Roofing rubber contains additives to inhibit growth of fungus and mildew, etc which can be harmful to the fish.
2) You stated that readings for ammonia and nitrites were "a little" off. Both ammonia and nitrites are highly poisonous to fish and can kill in relatively short time. Both readings need to be absolutely zero (0)!!
a) To help fix this problem: Stop feeding the fish until completely until the readings are back to zero (they will not die of hunger, but nibble on algae and plants instead).
b) Add a good beneficial bacteria product (see here:
http://www.pondmarket.com/catalog/index.cfm/category/77/beneficial-bacteria-slud) to help rid the water of these dangerous compounds
c) If all else fails do <b>partial </b> water changes each day (about 1/3 of the water, no more) until the reading goes down. Be sure to add a good de-chlorinator that also eliminates heavy metals (like this one:
http://www.pondmarket.com/catalog/index.cfm/product/807_79/pondmarket-koi-tlc-fo)
d) When readings are finally back to absolute zero (ammonia and nitrite) only add 1 or 2 fish at a time and check readings for a few days. The pond needs to grow a big enough bacteria culture each time fish are added to be able to neutralize the additional waste they produce.




---------- FOLLOW-UP ----------

QUESTION: Thank you for your response. All of the readings for the different pH, nitrite/nitrate, ammonia levels have been normal for about a week now but the fish continue to die. We got the liner from a reliable pond place but there is a possibility it is contaminated and leeching chemicals. How do we test for any other problems/chemicals? There is obviously something else wrong because they keep dying but we cannot figure it out. Everything has been testing normal for a while ever since we put in the chemicals to fix that stuff but the fish still die.

Answer
There has to be something that is killing the Fish. If not in the liner itself, then somewhere else in the Pond. You can try draining it, scrubbing it will solar salt and then refilling and draining several times to try and dilute whatever it is. After that, try just a couple of cheap small fish and see how they do.