That's what I was thinking. I don't remember what the rule of thumb I heard was, but that you basically shouldn't exceed 60% or 70% {or something ..
} of the rated capacity of the breaker (to account for start up surges)? So with the 10A breaker I was thinking of, no more than 6 amps of normal load (so maybe room enough for some powerheads as well, but not much more than that), or with Steve's 15A breaker, 9 amps of normal load.