Today is possibly the worst day of my life 
... My hands down favourite fish died today and looked like he went out painfully. I HAD a 5" wide reticulated male stingray in my 120 gallon and he was doing WONDERFULLY for 2 months straight, he ate extremely well, looked healthy and was very social. Hell, even today he looked perfectly fine and ate some blackworms right out of my hand. But about 5 hours after feeding him he finally passed after what looked like a seizure. He started to panic and he started darting up and down the glass and would sometimes just float on the surface and I'd have to help him down. I thought the water was too hot so I did a 20% water change and added some 7.0 PH stabilizer to help him out. I kept my tank at a constant 88 degrees for the past week and my stingray couldn't have cared less. So anyways after I did the water changes he finally calmed down after I detached his stinger from my net (had to use the net since he tried stabbing me, he's never done that before! he actually managed to nick me with it) So for a while he stayed motionless on the bottom breathing heavily...until he finally stopped, he stopped breathing and had spasms in his tail and mouth were vibrating alot. I tried reviving him by moving him above the air pump, until he finally died and the pain was gone when he stopped moving all together and he was dead.... I'm not going to lie I bawled my eyes out, this was a $100 fish that I saved up a few months for, not only that but he was very social and would race to my hands and climb all over them looking for food since he was hand fed. I really want to know how he died. From my investigation I ruled out water parameters since i have 240 gallons of filtration, do 20% weekly water changes as well as vacuuming substrate in the process, and add aquarium salt when needed. I even added aquarium salt a few days before this. I'm also ruling out my tankmates since he had absolutely no injuries or body deformations while this was happening. FYI my other tankmates are a 13" oscar, two 7" goldfish, a 10" bullhead catfish (getting rid of soon), 12" pleco, and a 7" Kelberi peacock bass. None of these fish EVER touched or nipped at him EVER if anything he was non-existent to the other fish. Right now I'm assuming it was the black worms I fed him. I ordered in some black worms from the LFS I bought him at, a LFS I know keeps their fish healthy. So anyways I bought a bunch for $20. But even then I change the water everyday while putting in NO chlorine, I take out the dead ones, and keep them in a fridge. But upon further inspection I found what looked to be leaches. They were shorter, flatter, much wider, and white compared to the black worms and I found about 3 of em. Could it have been the leaches that killed him? It seems as if he was specifically poisoned because my other fish were completely normal also because of the sudden death and spasms he was having because he looked like he was really stressed out. PLEASE PLEASE GIVE ME CLOSURE ON THIS AND TELL ME HOW HE DIED 
And anything I can do in the future to avoid this
... My hands down favourite fish died today and looked like he went out painfully. I HAD a 5" wide reticulated male stingray in my 120 gallon and he was doing WONDERFULLY for 2 months straight, he ate extremely well, looked healthy and was very social. Hell, even today he looked perfectly fine and ate some blackworms right out of my hand. But about 5 hours after feeding him he finally passed after what looked like a seizure. He started to panic and he started darting up and down the glass and would sometimes just float on the surface and I'd have to help him down. I thought the water was too hot so I did a 20% water change and added some 7.0 PH stabilizer to help him out. I kept my tank at a constant 88 degrees for the past week and my stingray couldn't have cared less. So anyways after I did the water changes he finally calmed down after I detached his stinger from my net (had to use the net since he tried stabbing me, he's never done that before! he actually managed to nick me with it) So for a while he stayed motionless on the bottom breathing heavily...until he finally stopped, he stopped breathing and had spasms in his tail and mouth were vibrating alot. I tried reviving him by moving him above the air pump, until he finally died and the pain was gone when he stopped moving all together and he was dead.... I'm not going to lie I bawled my eyes out, this was a $100 fish that I saved up a few months for, not only that but he was very social and would race to my hands and climb all over them looking for food since he was hand fed. I really want to know how he died. From my investigation I ruled out water parameters since i have 240 gallons of filtration, do 20% weekly water changes as well as vacuuming substrate in the process, and add aquarium salt when needed. I even added aquarium salt a few days before this. I'm also ruling out my tankmates since he had absolutely no injuries or body deformations while this was happening. FYI my other tankmates are a 13" oscar, two 7" goldfish, a 10" bullhead catfish (getting rid of soon), 12" pleco, and a 7" Kelberi peacock bass. None of these fish EVER touched or nipped at him EVER if anything he was non-existent to the other fish. Right now I'm assuming it was the black worms I fed him. I ordered in some black worms from the LFS I bought him at, a LFS I know keeps their fish healthy. So anyways I bought a bunch for $20. But even then I change the water everyday while putting in NO chlorine, I take out the dead ones, and keep them in a fridge. But upon further inspection I found what looked to be leaches. They were shorter, flatter, much wider, and white compared to the black worms and I found about 3 of em. Could it have been the leaches that killed him? It seems as if he was specifically poisoned because my other fish were completely normal also because of the sudden death and spasms he was having because he looked like he was really stressed out. PLEASE PLEASE GIVE ME CLOSURE ON THIS AND TELL ME HOW HE DIED And anything I can do in the future to avoid this 
