binomial GLMM with small upper limit

I am working with mortality data - the number of three animals per 
experimental unit that had died by week 1, week2, ... during an 
experiment.  So, I am using a binomial GLMM approach to model 
proportions with a random effect to deal with the repeated measurements 
from the same exp. unit.  (Specifically, I use the experimental unit or 
"Tank" as the random effect, since multiple observations from the same 
unit must be related... and there were temporal/spatial blocks, so each 
tank is nested within a block.  I include sample "Day" as a fixed effect 
in the model)

sm7<-glmer(predc.survtbl~predator*Day +(1|Block/Tank), 
family="binomial", data=predc2)

All is well, except the model suggests there are no treatment or time 
effects, while graphical inspection suggests there may be both.