Biopellets were invented for fish farming to reduce nitrate so that farmers can cram as much fish as possible in the pools.
Biopellet is very difficult to control as many factors affects its performance.
Over dosing, which is the common case, can lead to oxygen starvation, promote virulent bacterial growth and harmful to coral health.
Also not all biopellets are made equally, many are poor quality. Biopellets are very cheap and normally these cheap material are repackage for aquarium use with 1000 to 2000% mark up.
For carbon dosing, I will stick to vodka and vinegar. They are food grade and dosage is controllable.