Hey. So I have a 57 litre fluval flex tank. Problem fish dying. Originally this tank was home to a goldfish. I added some 4 netrite snails (as recommend to me for tank size) to help with the algae. About a month after the snails were added my goldfish died from what I thought was a swim bladder issue. I left the tank for about 8 weeks with just the snails as I couldn’t decide what to do, performed regularly water changes and treatment. As my water was sitting at around 24/25 c I decided to purchase a heater and venture into the world of guppies. Continued water testing shows Nitrate 20, nitrite 0, ph 7, GH 120, ammonia 0, KH 80. I have plenty of surface agitation so I wouldn’t have thought oxygen wouldn’t be an issue and the temp is 27/28 due to the weather. these levels have continued throughout and I have tested everyday. So since adding guppies 10 days ago they have continued to die one by one (I ordered 12 but got send 20) I haven’t fed them for 3 days now and when I was feeding was tiny amounts of food ensuring all food was eaten and would feed for around 30 seconds (maybe less). I’m down to just 7 fish now. They seem to be fine then almost kind of swell then die very suddenly. I’m at a loss. Could the snails have been carrying some kind of bacteria? I have also done a 20% water change everyday since the fish have been dying.
If the tank was left for 8 weeks the beneficial bacteria in the filter would have died back to just enough to support the snails. A lot more would be needed to support the guppies so I suspect ammonia/nitrite have spiked. What test kit are you using? Is it liquid based or is it paper strips? The snails are very unlikely to be the cause of the problem. Another possibility is that the water is too soft for guppies. They are a hard water fish and need the gH to be between 150-500 and preferably in the middle of that range. If you are using test strips though, your readings for all parameters including gH may not be accurate. Modern farmed guppies are also genetically very weak, and in many cases arrive carrying bacteria which has been suppressed when they were bred and grown on by use of antibiotics in the water. Once they arrive in someones tank, these bacteria can take hold, especially if parameters are off for the fish as well.