The problem is that you have way too many fish for the amount of water. They are producing a lot of ammonia which could kill all of your fish overnight. The water changes are probably helping but the copper sulfate is not doing anything. It is sometimes used to kill algae.

Do you have a test kit? It should be used very often until you get used to what is happening. Even then it should be used at least twice a month or whenever there is a change in temperatures, rain, water changes or anything else that can affect the pond.

You will have to get rid of some of your fish, add a chemical to neutralize the ammonia and/or add a lot of air to the water. I don't know what is available in India. The names of the products are different here. I use a combination of Activated Charcoal and Ammolock that I put inside the filter in a bag, a waterfall and two bubblers.

Your pond could possibly handle up to 10 mature Koi with sufficient aeration. That would be a waterfall, a splashing fountain, bubblers or a special aerator. I have a narrow but high waterfall and 2 large bubblers for my 1000 gallon pond. That is likely more than enough but I have too many fish as well. Your pond is almost 4000 gallons.

Your fish can be fed until it gets down to 13C. They are not eating because they are being poisoned by ammonia.

You don't say how deep the pond is. Koi need water that is at least 3 feet deep and 6 feet is better. The deeper water helps to stabilize the water temperature too.

I forgot to say, my pump runs at 2985 gallons an hour. That would be 11,299.5 liters an hour for 1000 gallons of water.

These posts are just so sad - I wish the places selling the fish could be more proactive about making sure they're going to a good home but no, they want to make more sales.

15000 liters =3962 gallons. Nearly 50 koi (doesnt matter if they're small now, they don't stay small) would require at minimum 500 gallons per fish or 25,000 gallons. Enough said.

True, it may be possible to set up some super-efficient system to allow more crowded conditions ... but that is quite beyond the scope of the average pond owner.

Kashka kat, did I leave anything important out? It is sometimes difficult to get everything said in a short post.

I agree that it is a shame that some dealers are not ethical. It makes new ponders give up.

Need help!

I have a 3,500 gal pond (10x15x3) with a 22� stream (containing two large and three small waterfalls and a bubbler/aerator) established in 2006. I have (had) roughly 30 or so fish. Five were ~10"-12" Koi and the rest are 6" or less Goldfish. I have not had any problems with the fish and have only had five die (two from predators) during this whole time. Then suddenly four days ago two large Koi died. Then the next day one more died along with the largest Goldfish. I tested the water and all results were almost exactly as they have been for the past few years � very consistent pond. I turned on the uv light and turned off the Iongen even though copper level was "0". I then added about 5 lbs of salt and the recommended amount of detoxifier. Everything was good until yesterday when another large Koi died along with two small Goldfish. Fish rep is at a loss. Aquascape rep said it might be a cold water parasite (thus the uv light). I have no plants as it is winter but do have a medium case of algae and that is why I had the iongen running for the last two months as I usually don�t need/use it except for spring startup.

Any suggestions/recommendations?

What a shame. There are several different possibilities but it is hard to pinpoint with limited info. We don't even know where the pond is located and that can make a difference. I always worry when Aquascape is mentioned but you say tests are within proper levels. Do you have rocks on the bottom? What kind of test equipment are you using? How old is it? Is there any possibility someone was spraying near you: pesticides, herbicides, fungicides, paints, etc.? Has there been a recent storm?

As I said, there are many possibilities.

The UV won't do much for a parasite that is already infesting a fish. You can use bubblers for added oxygen very effectively. Have you done any water changes? Added any chemicals? How are the fish acting? Have they shown any physical changes or symptoms? What is the water temperature? Are the fish grazing on a rock covered bottom with lots of mulm? Do you use Activated Carbon to detox the water? Is there debris in the water? Is there anyone who could have put something in the water that would act as a poison?( I had a contractor drop cigarette butts in the pond which my koi nibbled on. They died.)New plants around the pond that may be poisonous to the fish?

Hope this gives you some clues. Let us know.

My wife and I have a new plastic pond, with solar air bubblers, some rocks for letting the fish hide from the sun, and water lilies galore. We started with about 20 feeder goldfish and they lived for quite awhile. We thought it was the heat, so we devised a mesh canopy for shade and that worked for awhile too. We fed them every morning, and they were energetically eating what we gave them. We were losing about 10 fish a month! I think the water got too warm here near Fort Walton Beach, Florida. They stayed on the bottom after the 1st month; and would only come up for feeding. They were growing in size too. What's happened to all 2 dozen fish?

There could be a number of things but address the heat first since that concerns you. What exactly was the water temperature? Comets(goldfish) are cool water fish. They need deep water to stay cool. How deep is your pond? Partial water changes can help.

Feeder fish are not always the best bet. They are culls (and the reasons for culling are not always obvious). The smaller they are, the more chance they will not survive. That is why they are so cheap. Fewer but larger fish may be the way to go, but an adult comet, 6 to 8 inches long not counting tail fins, requires at least 50 gallons of water, each.

You don't mention a pump or filter. Do you have such a system? Water that is too still will develop toxic areas where anaerobic bacteria thrive. A pump and filter cleans and oxygenates the water which is important. Aerobic bacteria live all through the pond but it works best in the filter medium to break down bad stuff in the water. Do you have rocks on the bottom? Even without other problems, bottom rocks can trap mulm, uneaten food and other debris that can kill fish.Rocks should either be removed or be cleaned very frequently.

Do you test the water? Tests give you a clear warning of water problems. You can sometimes get the water tested at the place you got your fish. Once you have the test results, tell us here rather than adding all the chemicals the dealer may suggest. We may be able to tell you what to do without spending all that money and not doing any good.

We can help you better with more info such as the size of the pond, any additives you put in, etc.