Hi, I have a 40 gallon heavily planted tank with crystal red shrimp, glass catfish and a few other species that are all thriving, and have done for the last couple of years. I recently bought 5 assassin snails from my local aquarium centre hoping that they would help to keep my ramshorn snail population down. Unfortunately within 24 hours all 5 were dead at the bottom of the tank! I contacted the shop I bought them from and they suggested I might have copper contamination, so I bought myself a testing kit but it showed absolutely no trace of copper in the water. I figured perhaps the assassins were a bad batch from the shop so I bought another 5 from ebay hoping to have more luck. They arrived next day looking healthy, but then within 24 hours they were all dead , again! The thing that really has me stumped is that all my shrimp, ramshorn snails and other inhabitants are so healthy, yet I can't keep a few supposedly hardy assassin snails alive for 24 hours. One thing I would mention is that my pH is quite low at around 6.2 and my Kh is around 0.5. I also use pressurised Co2 on a timer for around 7 hours a day. Someone has also told me that a low pH can erode the snails shells, but surely it isn't enough to kill them within 24 hours? Especially when the ramshorn snails don't seem to have a problem. One last thing I should mention is that I do use standard flourish around once a week and wondered if this could be having an adverse affect? Any advice or help would be appreciated as I don't want to give up on eventually being able to keep assassins in my tank.