Dead pleco, how did it die

[Fishie boy]

Hi all,

I recently bought a pleco, but yesterday it died. It was timid but it did move around the tank and commonly stayed on the driftwood or underside of a leaf. I treated my tank for fin rot last week as two of my guppies had lost some tail, the treatment said it was safe for scaleless fish. I took a water sample and the fish to my pet store and they said it was perfect but they didn’t know why it had died. I’m worried for my other fish as I also have some peppered Cory catfish.
My water parameters and photos are below:
Temp: 25C
pH: 6.8
NO3: between 0-10mg
NO2: 0
Ammonia: 0
GH: 8d
KH:6d
Cl: 0




Thank you for any help you guys give!

 

[the loach]

It's impossible to say what caused his death. What kind of test kit did you use for the ammonia? What kind of treatment did you use?
Please don't get another pleco, they grow over 20", the fish rescues can't take them all and they are now an invasive species in the south.