2 Plecos Dead Within 1 Week

[FishyFishy11]

So I just bought a new zebra pleco around 3 days ago. I saw him eat some algae wafers and fish pellets. He was active and healthy from what I could tell. I woke up this morning and he was dead. What is the reason for this? Ammonia and Nitrites are 0ppm. Nitrate is around 2-5 ppm, and ph is 8.2. Any help would be nice.

 

[shellyx]

Are you buying them from the same lfs?