I have an 8g tank with some fry, 2 mystery snails and an outrageous amount of pond snails and MTSs. Lately the pond snails have been dying off. They float about fully stretched out of their shells 2 or 3 at a time, then die, then more start doing it. F4A told me a while back that coming out of their shell as much as possible in mystery snails can often mean poisoning, so even though it wasn't the mysteries I tested the water:
ammonia - 0
nitrite - 0
nitrate - 40
ph - 8(ish)
temperature - 22
The tank has been running for approx 6 months.
As there are no plants in this tank I find that nitrates are much higher than in my planted tanks but this has never been a problem before. I do 25-30% water changed every 3-4 days because the filter is quite weak due to the fry.
Since this has been happening with the pond snails I have been doing 10-20% water changes every 2 days and nitrates have went down but they haven't stopped dying.
There have been no medications added other than melafix.
I'm worried that something is going to start going wrong with the mysteries since the pond snails have started all dying off.
Does anyone have any ideas what could be causing this? Like I mentioned I suspect some sort of poisoning but I can't think what from. I can't think of anything else that has been put/could have got in the tank but if anyone has seen this before I'll rack my brain to think if there's any possibility "x" could have gotten in. On the other hand, as much as I'm not much of a fan of meds, should I maybe use soemthing to kill off any potential "nasties" that could have gotten into the tank that won't harm either the fry or the mysteries?