Sorry but bettas should be offered their food once a day. PetCo says that because at cool tempertatures the fish slow down and don't need to much food.
Plecos should be fed once a day. I would add a second tablet if the guppies steal it.
And if the betta dosen't get any food you should put him in a jar of his own.
Who am I? Well I am a Junior Member of the International Betta Congress and a breeder of white HMPKs, red dragon HMPKs, black/red dragon HMPKs, metallic multi HMPKs, blue masked HMPKs, and now multi color HMs. Soon to add black HMs. I will be showing in New Breeder class in fall of 2012.