is my pleco getting enough to eat?
 

I have a five inch pleco, and as is apparently normal for them, he isn't very active during the day. every evening, right about the time i turn off the light, i drop an algae waffer in for him, but i can't tell if he is eating it, or if the tiger barbs and swordtails in the tank with him eat it all before he gets to it. should i be worried about him not getting enough to eat?

Which species? Most are nocturnal or mainly nocturnal. I would drop in the sinking food well after lights are off, so the upper fish are basically settled and in sleep mode. The pleco will find it in total darkness.

i'm fairly sure it is a common pleco.

and feeding him when the lights have been off for a while is a little difficult, since the tank is at the office i work at and i turn of the light when i leave for the night.

I feed mine sliced cucumbers once or twice a week... I know it's him eating it because I see him attached to it... and when I come back to see him I just see the edges of the cucumber remaining. You can try that. I have one of those plastic clips with the suction cup attached to it that I use to weigh the cucumber down.