I've done it many times, I'm afraid. When I top off the pond now, I don't dare even wander off to go pull a weed for fear I'll forget & leave the water running for hours.

I agree, these fish could well have been ill when you bought them. The same thing has happened to me recently when I tried to introduce some minnows (striped shiners) into my 55g indoor aquarium. Deaths at a high rate, signs of distress, and ultimately, all died within two weeks. In the end they were patchy, discolored and coated in fungus. :( You don't say much about your pond set up, or how you introduced the fish. I know my biggest problem when I put the minnows in my tank, is that I did not account for temperature needs. The minnows, being cold natured fish, could not survive in my tank seeing as the water was warmer than they were used to and therefore less oxygenated. Even with an air stone and filter, they could not get enough oxygen. The stress from moving only magnified their existing problems - which were plenty, seeing that they were bait fish and were not babied as most pet fish are. Add to that fact that my water conditions were less than ideal for them, their death was pretty much assured. In the future, I will do more careful research about the fish I introduce to be more certain of their needs (rather than assume), and only choose healthy specimens from a reliable source. Plus, checking and rechecking my water parameters before putting them in, and introducing them in the gentlest way to minimize the stress. Sorry about your fish, good luck in the future though!

I absolutely believe plants can clear green ponds...have posted that many times. The myth is that this is done buy higher plants. One of the simpler things to show as a myth. A green pond has what level of ammonia and nitrate? Certainly that's easy to test, anyone can. Or a person can read lots of research on this for fish farms and other farm type ponds done by the ag department adn many Universities. A green pond almost always test to 0 ammonia and nitrate. Why? Because it's green. Algae is a plant (for our discussion anyways). Plants use ammonia and nitrate to produce new cells. Millions of green cells appear in a pond guess where they got the ammonia and nitrate? Now you have million of green cells floating around waiting for one thing in order to divide...more ammonia or nitrate. You have a water column filled with these cells just waiting to bump into an ammonia or nitrate molecule. When it does it can split (oversimplification sure). The myth says if you add higher plants to a green pond they will clear the water by out competing the algae for these nutrients. This myth only seems believable to people who do not test for ammonia/nitrate. If a green pond is already at 0 ammonia/nitrate...so how does it starve these millions of algae cells? For some unexplained reason the myth purveyors ignore the elephant in the room...algae is a plant. So why doesn't the algae starve itself to death. If you believe the myth and don't want it disproved the only possibility must be the higher plant must out compete the algae. Mine you I've never read any promoter of this to ever offer any data from any study about this. Their proof is purely deductive reasoning, which is fine if the deductions are true. But they aren't. Say we place a potted plant in the pond. Ammonia comes out of a fishes gills. That ammonia molecule has to float by thousands, maybe millions, of algae cells who are just begging to suck it up. For the myth to be true these algae cells would have to be very polite little creatures.Now our little ammonia molecule has to get into the pot's media...so easy task. But say it does...now the higher plant can suck it up and millions of the poor algae cells starve and die. Killed by politeness. When the algae all die those nutrients are released. But for some mysterious no algae decide to use these new nutrients...only the higher plants. For this deductive reasoning to be valid a green pond would have to be rich in nutrients and a clear pond void of some key nutrient. And I think many people believe this to be true and so self evident they do not need to test the water or even do some reading. And of course many people today believe science and data is all a big hoax. But anyone who has ever measured the nutrients in green and clear ponds will very quickly find out is the opposite is true. A green pond is extremely low in key nutrients and a clear pond very or extremely high. More evidence we can deduce. Many people report adding plants and within a short time the pond suddenly clears. Sometimes overnight. Wow, the added higher plants sucked up all the nutrients and killed all the algae in hours. For this deduction to be true at least 2 things must be true. First a key nutrient level must be zero. If the water is tested it probably will be zero ammonia.nitrate, because it was the day before too. Oops. One problem with that, it isn't how plants work. Many people seem to think these key nutrients like ammonia/nitrate are like air. If we don't get air we die in a short time. Algae died in a short time so nitrate must be like air. Or maybe people think nitrate is like food is to us. Closer, but we can live for a long time without food, algae can't. Well, nitrate isn't exactly like our food, it's a nutrient, not a calorie. Nutrients are needed to build cells. For us that means new skin cells, bone, etc. Algae use it to make new cells, to reproduce. They, like us, can live for a really long time lacking nutrients because their structure, like ours, has already been built. A tiny amount is needed to run processes, but mostly for cell construction. You can take as many multivitamins as you like, but if you don't consume calories you'll die in around 3 weeks. Algae get their calories from photosynthesis so they can live for a very long time without nutrients. So the higher plant starving algae theory has some massive holes that promoters never explain. They don't really have to because pond forums are full of people who believe the same. Fact is proven by popular vote which is becoming more accepted as fact these days....thank you internet. But there is one deduction that is true...adding plants to a pond does sometime clear a pond. Many people have posted this and I've seen it myself more than a few times. It's obvious to anyone doing basic water testings that it sure as heck can't be the higher plants starving the algae because the tests prove the opposite. What could it be? A long time ago a dude name Norm Meck made a really ground breaking discovery and published his findings. He found that water from a clear pond can be toxic to green water algae. He described how he did the experiment so others could repeat the experiment to see if they got the same results. I've never read about anyone else ever bothering, most people are much too busy repeating myths in forums, but I did. And I found the same thing. Something in the water killed the green water algae. Where did this toxin come from? Norm's theory was a bacteria produced it so the dead algae cells could be eaten. Not a bad theory, not great. Killing a pond full of algae so this bacteria could eat for a day or two doesn't seem like something nature would do. But a reasonable theory for it's time (thousands of years ago in internet years). Norm's experiments inspired me to do more experiments. This was before UV filters were common and cheap so green water was an actual problem. I set up a bunch of small tanks on the roof of my San Jose house and started growing green water algae. Full sun and I'm adding lots of fertilizer to water. I'm getting water that looks like green paint. I'm experiment away and getting nowhere. I found a filter that would clear green water...it was amazing...but then it completely failed other times (had to do with algae lifecycle, another story). It was a roller coaster ride. I was kind of giving up. Well I had some Pennywort I was wanting to reproduce and I had a bunch rooting in styrofoam cups...where to put them. I put a bunch into one of the test ponds. Green water wouldn't hurt them. A week or so later I went up to the roof to top off the tanks and the tank with the Pennywort was clear. I do the Meck test and sure enough the water was toxic to green water algae. At that time my best (only) theory was Norm's, it was bacteria. Well there was a lot of string algae in the tank from the Pennywort, darn stuff gets into everything. So I pull a bunch out threw it down into one of my ponds. It was a good handful. I tossed into a pond that at the time had a deep gravel bed maybe 6-10" of water above the grave which was 16-18" deep and the water was green. I just threw the string algae in there because I didn't want it on the patio, lawn flower beds, and it would be easy to fish out later. The next morning the pond I'd tossed the string algae into was clear. That pond was about 900 gals and at the time had no pump or filter and had been green the entire time I had it, more than a year. This is the time when you stare at something and run through every possible related thing from your past that might explain this. I couldn't come up with a theory. Testing nutrient levels came up with the same results and the Meck test showed the water was now toxic to green water algae. The bacteria theory seemed unlikely to me now. The string algae was the one common factor I saw in my limited experiments. So I started experimenting with both green water algae and string algae. I had terrible results. Sometimes the string algae cleared the green water but many times the string algae died. It was tough going because string algae takes a long time to appear dead. And I was having a difficult time growing both string algae and green water algae. And I kind of lost interest because by now my filter had cleared my pond and that was good enough for me. Years later I started reading about research about allelochemicals, stuff plants create to fight other plants. Growing up I knew some plants did that, like Black Walnut trees killing grass beneath it, but never made the connection to algae. The research was finding more and more plants doing it and many people were starting to think this was very common in the plant world. I made the connection then and researched algae. Unfortunately the only research I could find was done on marine algae and they did find they were producing chemicals toxic to other plants. Not directly related to freshwater algae but a pretty darn good theory. Then I started reading old pond forum posts, archived stuff. And I saw the string algae pattern over and over. People adding plants, seeing their ponds clear and then awhile later asking about how to get rid of string algae. They never made the connection between adding plants and the string algae because of course there's no visible string algae on the plants because the seller always pulls it off. But little bits and spores are certainly present. I also read about Trickle Towers which were popular at the time. TT are used to remove ammonia but many people were reporting their ponds cleared. There were lots of theories but nothing that made much sense. But people were also talking about string algae growing on their TT, saying they'd never had string algae before. And even further back people who added streams were seeing their ponds suddenly clear followed by reports of string algae in the stream. I started asking people in forums complaining of green water if they had string algae. In most cases people had one or the other, sometimes both but never full blown string algae. While it hasn't been proven I certainly believe string algae is the source of the toxin and responsible for ponds suddenly clearing. At least I haven't been able to think of any holes. And every year there's more and more research into allelochemicals that keeps pointing to the same conclusion. My theory is green water algae use both resource competition (blocking sunlight) and allelochemicals to fight against at least some species of string algae and maybe other macro algae. The string algae is probably mainly just using allelochemicals against the green water algae. In order to win the string algae has to get a foot hold near the surface of the pond so green water algae couldn't block as much light and weakening the string algae. Tops of marginal plant pots, streams, TTs, my shallow ponds (the test ponds were about 6-10" deep). I believe that string algae is the plant causing green ponds to clear and it has nothing to do with higher plants or them starving algae to death. It fits way better anyways at least until someone shows there are holes in the theory. The real answer may come from aquarists. In the past few years some aquarists have been adding separate tanks of string algae and have seen clearer water. These guys are pretty serious and do a lot of testing. Most believe the nutrient starving theory although their tests show otherwise. I think they're assuming its a micro nutrient, but they have all the same holes as the high plant theory. There is at least one aquarist pursuing the allelochemical theory. And he has been testing other underwater plants that may also produce allelochemicals. It fits that any underwater plant might need such a weapon. I know must everyone stopped reading long ago, and I too don't really care any more about why ponds clear. We have cheap UV filter now and that's that. The one thing I still do find fascinating is why people still push the higher plant myth. It is just so easy to disprove. Why not repeat some other theory that's at least harder to disprove? To me that's interesting. My wife is on to me wasting time in pond forums again so I bid you a good day. Sorry, but I didn't have the time or desire to proof read this and make corrections.

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.