How to remove spike from the data series?
I would put this in a comment but I don't have enough rep points, as just started on this.

I would recommend reading this information before designing with sigma-delta ADCs
http://www.numerix-dsp.com/appsnotes/APR8-sigma-delta.pdf

It may be that you need a basic analog filter before the ADC input to prevent interfrence noise aliasing back in to your signal (assuming the load on your cell is constant?).