I sure learned my lesson on this topic. Months ago when I had my original aquarium setup, we went away for a week and a half, so I bought one of those feeder block things. I came back to a cloudy tank, and the feeder block had a slime coating on it. The water looked murky & thick.... gross. I learned afterwards that those feeder blocks are held together with plaster of paris!!!!!

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So the next time we went away, I got this automatic feeder, it worked great. I'm sure they'd have been ok without food as well.