I apologize in advance for this "lengthy" post! I have a 55-gallon goldfish aquarium that has been set-up for about 5 or 6 years. I have always been confused about our water. We live in a rural area, so our only water source is "well water". I frequently see posts about tap water, but it appears you are only talking about city water. When I first started, I had a 20-gallon tank and I purchased water from my LFS. When the fish store closed, I bought bottled spring water. Then when I decided that I wanted the 55 gallon, it was no longer practical to drag home water. The new LFS guy told me that I should be able to use our well water, so I did. The problem with that is that our hard water bypasses the water heater, so we only have cold hard water. I used to fill large Culligan bottles and let them set for a few days for the water to warm up to match the tank water. After about a year of this method, I injured my back and could no longer handle these large bottles. I was about to give up fish keeping all together, when I read about the Python Water Changer. I asked my LFS if I could use water cycled through our water softener for the fish. It seemed odd to me that this would be O.K., but I have been doing it for at least a year and a half. My fished seemed to do very well, but for the last 6 months I have had a lot of death. The LFS guy said that when I was buying bottled water that it was deinonized, which in turn stripped the water of a lot of minerals that goldfish need in order to survive. He then suggested adding electrolytes which seemed to help. I didn't seem to have a lot of problems when using the hard water, but I constantly had to clean brown algae from the plastic plants and ornaments. Now that I am using softened water, I don't have any brown algae, but I am constantly fighting green algae. So I asked the LFS why green algae has become such a problem when I never had it before. Then he tells me to use a phosphate remover in the filter and to change my light bulbs. That slowed it down, but I still have to use AlgaeFix about every 3 or 4 days to keep it under control. I have repeatedly tested the aquarium water for pH, ammonia, GH, KH, nitrate, and nitrites. All of the tests are within safe limits. I have never had more than 4 or 5 fish in this tank, so ammonia or overcrowding is not the problem. I do weekly water changes of about 25% to 35%. I have an Emperor 400 filter and I use StressCoat, Amquel Detoxifier, Electrolytes, pH Adjuster, and Algaefix. I do use aquarium salt to a low extent, because I don't know how much salt is already in the water because of the softener. I know that I don't overfeed. It seems I can't keep my fish alive anymore. Recently, the one that lastest the longest was for 4 months. When they get sick, they begin by flashing a lot and then they lay sideways on the bottom gasping, with their gills pumping profusely. Then they try to bury themselves in the plants and ornaments. By this point, I usually euthenize them by freezing because it is too painful to watch them suffer. It seems to me that these symptoms represent a toxicity in the water, but again, the water tests are fine and it only happens to one fish at a time. The others appear healthy. I have stopped replacing the ones that have died and now I am down to only one fish until I figure this out. Is my water softener killing my fish with some chemical that I'm not aware of? Is the salt in water softeners toxic to fish? Can I try using half hard water and half soft water for water changes? I am at the end of my rope and I would really appreciate any advise that anyone can give. After years of searching, I came across this site today. It is the first one that I have seen that I am completely impressed with. You all seem to be experts and God knows I need an EXPERT! Thank you.