life or death situation

i split my 55 in two for two groups 5 half inch bgjd for a breeding project. i want to put a few corys in each side to keep the extra food cleaned up cuz its kinda hard for me to get used to feeding only those few little fish. will the dempseys kill the corys at a certain size, i heard the get aggressive at about 4 inches, or is their another type of critter i could keep with um to keep the water quality up? i do a lot of wc's thats not a problem but i have had prblems with nematodes in the past and would like to avoid that mess at all cost... just cant take the little boogers staring at me all wantin food
need some suggestions [help]