Rip Green Phanton Plec

[San O Fisher]

On saturday I did a 40% water change same as I always do, but I ended up doing a massive cutback on my plants and ripped a few out that had not been as doing as well as the others. I added my natural aquarium vital and my plant food as always, then fed the fish later about 30 minutes later. I came back 10 hours later to find my green phantom plec belly up and bloated dead on the floor and all my fish including my syno eupt at the top of the tank gasping for air...I did not check water stats, but quickly did a water change of about 50% and within about 15 minutes everything had settled down, in the morning every one was acting normal. I didnt even lose a tetra or an oto, which I figured I would at least have lost a couple.

any thoughts? also, I will be looking to get a new plec, but have not decided what I want yet