In my pond, I use straight city water (perhaps good water in Voorhees, NJ) and I never had any problem with chlorine. I never lost a fish either. Essentially, I do not like to use any chemicals like chloramine etc. However, I use a small quantity (one lb per
1000 gallons) of iodide free salt. I also add pond-zyme plus made by PONDCARE. I last bought 8 oz for $12.00 from Petsmart. I only use approximate 2 oz every few weeks. I do have a Laguna UV sterilizer 24/7, Laguna skimmer/bio-filter and a half a dozen plants. I also have a backup sand filter. I have a 6000 gallon pond for about five years with approximately 20 large fishes: koi, comet, and two very large albino catfish. I do not have any floating algae.
My suggestion is to use some kind of biofilter and pond-zyme plus. Let the biofilter establish for a couple of weeks also the bacteria in pond-zyme, then add an UV for pond. Laguna system is cheap and worked quite well for my pond. Of course there are a lot of high tech systems(Bakke, bead-flter etc.) and chemicals. But in this board I read about lots of problem with water gardening. I wonder whether that is partly due to overuse of chemicals. I must admit that my five-years of water gardening experience is certainly not long enough. There are more experienced people here, they could give you alternative opinions. Good luck!!