Posting about a very unfortunate event in hopes of maybe preventing it happening to another keeper in the future. As ultimately this was on me. This will be a long story. To start, this occurred in a 1000gal pond with 2 RTC, 3 TSN, 1 hybrid, 5 oscar, 1 gar, 2 black sharks 2 plecos and a few other stragglers. I spend an incredibly large amount of time watching these fish / obsessing over optimum water quality. If anything is slightly wrong with a fish, I will notice immediately. A couple weeks ago I fed my fish like normal on a thurs night, everything was normal and fish as they always were behavior wise. Friday morning my hybrid was hanging out by the surface holding his mouth slightly open, not gasping for air or anything. Still swimming around if disturbed, but odd. Went to work came home that evening, the same hybrid was now resting ontop of block that was allowing his back to be out of the water, this was very odd and concerning for me. That hybrid was always the first fish to eat so I decided to feed a small amount to see what would happen, he did not eat. The TSN all ate ravenously. Now I’m really worried, next morning I go out and he is upright sitting in the bottom, but something told me to touch him, he was dead. Us big fish keepers all have those few special fish in the bunch they would truly not want anything to happen too, this was one of them. 
I took the fish to work with me (veterinary technician) and necropsied it in hopes of finding some blatant answer. Fish was pristine, 4.5 lbs at 1 year old. At this point my mind is going all over the place from oxygen levels too potentially tainted city water and and whatever else, but in those cases one could assume all fish would be showing some symptoms. Saturday night I get home to find one if my TSN upside down on the bottom, not dead, but dying yet if I tried to grab the fish it would flip over and dart across the pond. At this point its 9pm I’m freaking out and have multiple hoses and a pump draining this pond for a emergency water change… while that was happening I was holding the TSN upright over a large air stone that happens to be directly next to the pump (keep this in mind). If I let the fish go it would swim after a moment to leave that spot and then stay put. The only spot it refused to stay was by that pump… yet in my panic I proceeded to hold that fish over the air stone for at least 45 minutes until I accepted it was dead. I decided I was only going to fI’ll the pond halfway in case it was oxygen related or city water related, to allow for way more surface agitation and less water just in case. I go inside around midnight and check the pond again at 2 am, first thing I see is another TSN upside down dead on the ground!!! WTF 
at this point I’m defeated af and had to go to sleep expecting more casualties. There weren’t anymore. The next day at work it freaking hit me. 
This is where I messed up. For at least 2 months, when I stuck my hand in that water, I would get the lightest of tingling sensation…BUT only if I had picked my fingernails short exposing that sensitive skin(which I do often). This originally made me quite concerned but seeing as how I had made my girlfriend stick her hand in a countless occasions and all the fish acting fine I figured there’s no way, if there was any electrical current in the water all the fish would be freaking out or dead!!! So I thought. Naively I let the pond run and convinced myself I was crazy. That day I ripped off all my fingernails and the moment I got home I stuck my hand in and felt the sensation, but it wasn’t consistent literally just an initial tingle upon entering the water only in my fingertips… then I stuck my hand in the pond next to it and nothing.. repeated this process and then unplugged the pond pump and stuck my hand back in. NOTHING 
My pump was 100% putting electrical current into the water that entire time, and I’m still not exactly sure as to why those 3 fish all died suddenly within 24 hours and no other fish was affected. However, those 3 fish were the fish that held that corner down and spent the most time by the pump. Idk if they were just slowly being affected until it was too much to handle or what, but I know that was the cause of death. Now that I have a new pump running that isn’t faulty, there are fish on all areas of the pond, specifically near that pump, that were never over there. They knew not to hang out over there I guess. It’s still incredibly odd to me that other fish weren’t affected but am glad to have found the cause before it got any worse. I guess the moral of my story is, obsessively pick your fingernails to notice potential electrical current in your water and don’t ignore it.
I took the fish to work with me (veterinary technician) and necropsied it in hopes of finding some blatant answer. Fish was pristine, 4.5 lbs at 1 year old. At this point my mind is going all over the place from oxygen levels too potentially tainted city water and and whatever else, but in those cases one could assume all fish would be showing some symptoms. Saturday night I get home to find one if my TSN upside down on the bottom, not dead, but dying yet if I tried to grab the fish it would flip over and dart across the pond. At this point its 9pm I’m freaking out and have multiple hoses and a pump draining this pond for a emergency water change… while that was happening I was holding the TSN upright over a large air stone that happens to be directly next to the pump (keep this in mind). If I let the fish go it would swim after a moment to leave that spot and then stay put. The only spot it refused to stay was by that pump… yet in my panic I proceeded to hold that fish over the air stone for at least 45 minutes until I accepted it was dead. I decided I was only going to fI’ll the pond halfway in case it was oxygen related or city water related, to allow for way more surface agitation and less water just in case. I go inside around midnight and check the pond again at 2 am, first thing I see is another TSN upside down dead on the ground!!! WTF at this point I’m defeated af and had to go to sleep expecting more casualties. There weren’t anymore. The next day at work it freaking hit me. This is where I messed up. For at least 2 months, when I stuck my hand in that water, I would get the lightest of tingling sensation…BUT only if I had picked my fingernails short exposing that sensitive skin(which I do often). This originally made me quite concerned but seeing as how I had made my girlfriend stick her hand in a countless occasions and all the fish acting fine I figured there’s no way, if there was any electrical current in the water all the fish would be freaking out or dead!!! So I thought. Naively I let the pond run and convinced myself I was crazy. That day I ripped off all my fingernails and the moment I got home I stuck my hand in and felt the sensation, but it wasn’t consistent literally just an initial tingle upon entering the water only in my fingertips… then I stuck my hand in the pond next to it and nothing.. repeated this process and then unplugged the pond pump and stuck my hand back in. NOTHING My pump was 100% putting electrical current into the water that entire time, and I’m still not exactly sure as to why those 3 fish all died suddenly within 24 hours and no other fish was affected. However, those 3 fish were the fish that held that corner down and spent the most time by the pump. Idk if they were just slowly being affected until it was too much to handle or what, but I know that was the cause of death. Now that I have a new pump running that isn’t faulty, there are fish on all areas of the pond, specifically near that pump, that were never over there. They knew not to hang out over there I guess. It’s still incredibly odd to me that other fish weren’t affected but am glad to have found the cause before it got any worse. I guess the moral of my story is, obsessively pick your fingernails to notice potential electrical current in your water and don’t ignore it.
