My 1st post so excuse any mistakes! We have had a tropical tank for over 2 years and have managed to overcome most problems by searching Internet forums such as these but I'm at a loss as to what's happened.
We have a 64l tank, not planted and up to 3 months ago kept 4 mollies, 2 swordtails and 3 tetras (so I wouldn't say overstocked). The trouble came when 1 of the swordtails became sick 3 months ago. Sorry, I can't remember details but I added some methylene blue to try and save it but measured it wrong and the tank went black
I did frequent large water changes initially but lost both swordtails and a molly (the Molly had looked not right for about 12 months though) My filter also stopped working.
Unfortunately, around this time I slipped a disc in my back and water changes had to become less frequent and I couldn't bend and twist to change the filter. Even so, we noticed a baby Molly in the tank about a month ago which I took to be a good sign!
Last week I did another water change (approx 30%) and bought a new filter. Everything seemed fine in the tank, no signs of illness and looking less blue but I got up this morning to find 2 of the mollies dead. I've tested the water and parameters are absolutely fine. Surviving fish look ok but I'm very sad and worried that I've harmed the fish in some way.
Any thoughts or ideas of what might be going on?