Hay all ... I apologise if this is in the wrong place ... I am new 2 this forum ... I have a strange problem ... I have a 220L <58 gal> community tank with mixed tetra's, sword tails, albino rainbow sharks and 2 pleco's < 1 hi-fin and 1 unknown > and a pearl angel, my problem is this, About 3 - 5 weeks ago I did a 35% water change as I do every 2 weeks <I was told I can do it every 2 weeks due 2 having a lot of filtration>, during the water change I added a small rock formation of quarts <boiled 2 clean> and I added the required antichlorine etc. Shortly after this water change my angel fish looked like it was bleeding internally around its mouth ... about a week later it died, I did another 30% water change as instructed by my LFS and after this 3 fish <1x sword tail, 1x black tetra, 1x albino rainbow shark> developed swim bladder ... All the readings are correct < I dont have test equipment so my LFS did the tests 4 me > and I have not changed their diet, what could be causing this ?? All comments are welcome and I thank You all in advance.