What's their temp? Remember that temps drop during seasons and especially at night. Rapid and constant changes are very taxing on them and can make them very sick.
Also, I would definitely supply them with extra food. It can be as simple as clipping a slice of zucchini or cucumber to the sides, or tossing in a feeder block (beware as they can mess with waste levels and ph) or algae chips.
I have 3 otto cats, small 1.5 inch sucker, in my 20 and I make sure to offer extra food.
How large is your tank? Most tanks won;t supply enough food to support that many suckers unless it;s a very large one. You say office, so I suspect it's on the small size. You could keep some algae wafers/chips in your desk and toss them in every couple of days.
And you say tank, that means you have aeration/filtration, right? Some Pleco's are capable of living in low oxygenated waters (sacrificing stomach space for breathing), but only certain breeds and only in low, so some aeration/filtration is definitely required.
Best of Luck!