It sounds as if your horizontal stab has negative incidence relative to that of the wing. If the stab is glued in, this can be quite a job to fix, requiring cutting the stab loose and resetting the incidence. Correct stab incidence is very important, since you can't trim out an incidence error, except by the use of elevator trim tabs, something I am using increasingly on my own models. Otherwise, I avoid glueing in the stab, attaching it with bolts so that it can be shimmed a bit to correct those almost unavoidable small incidence errors. I have also warped the stab to get its average, effective incidence correct, which can only be determined by careful flight testing, but this can also be very tedious work.