Okay, i just noticed that my fish are acting strange and all staring in one corner. I have 12 fish in total, 2 Angel fish and 10 Discus. The angelfish seem to be fine but the discus are acting really weird. I also tested the water after i did a 50% water change as soon as i saw the fish going crazy, the pH is now 7-7.2(can't really tell which) and the ammonia is 0.5, the nitrate is at 0. I had the tank setup for about 8 months or more and they never acted like this. Before this happened, I changed 50% about every 2 weeks and then i add Stress Coat and Stress Zyme. When i was changing the water, i noticed one of my heaters broke and as i was attempting to take it out, half of it fell in the water (maybe this is wat caused this to happen?). I quickly picked it up and threw it away, but i made sure nothing was left from the glass breaking. I also added Epson Salt to the tank which i usually dont do but i heard from my uncle that it helps the fish. Now the fish look like they are all going to die(i hope not!!!) and one of my small blue diamond is on the gravel swimming on its side and its almost like if it has no power to swim. Also, i noticed while i did the water change the discus were spitting water? They had their mouths faced up and started to spit water. Please help!