Well, cichlid pellets do not have ingredients that will harm other fish. Just that the formulation is different to perhaps enhance the growth and colours of cichlid fishes. I have been feeding tetrabits (with a picture of a discuss fish on the pack) to my cichlids. For the guppies, they will probably benefit from the higher protein and colour enhancing ingredients from the pellets. So, no problem. Unless the guppy chokes on the pellets or cannot digest (depending on the size).

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The nose runs and the feet smell - go figure
Steven