I cant understand how do You plane to remove
DC offset.
Sdditionally some notes:
1.
//y[n] =(0.996 * y[n-1]) + (0.996 * x[n]) - (0.996 * x[n-1])
I'm missing something or
//y[n] =(0.996 * y[n-1]) + (0.996 * x[n]) - (0.996 * x[n-1]) ===
==== 0.996 *(y[n-1]+x[n]-x[n-1])

Anyway this cannot be correct - check that appnote -
filter has different coefficientsfor different members of
expression:
y[n]=a.y[n-1]+b.x[n]+c.x[n-1].

For example: http://www-users.cs.york.ac.uk/~fisher/mkfilter
high pass filter, sample rate 50hz, stop freq=10hz:

/* Digital filter designed by mkfilter/mkshape/gencode A.J. Fisher
Command line: /www/usr/fisher/helpers/mkfilter -Be -Hp -o 2 -a 2.0000000000e-02 0.0000000000e+00 -l */

#define NZEROS 2
#define NPOLES 2
#define GAIN 1.088114353e+00

static float xv[NZEROS+1], yv[NPOLES+1];

static void filterloop()
{ for (;;)
{ xv[0] = xv[1]; xv[1] = xv[2];
xv[2] = next input value / GAIN;
yv[0] = yv[1]; yv[1] = yv[2];
yv[2] = (xv[0] + xv[2]) - 2 * xv[1]
+ ( -0.8425385784 * yv[0]) + ( 1.8335456400 * yv[1]);
next output value = yv[2];
}
}



2.Your filter is something like low (or high?) pass filter
How this helps to eliminate DC offset?

3.As Russel says "outputting 50 values a second is overkill"

4.From where You get these 200 microseconds period for
sampling?

5.There are much better micros for poweremeter, specialized too.

regards,
Stefen