It sounded like you wanted to turn off the additional weight added for the Tare Weight ...
To turn off the display of weight there are several switches ...
There is one for each of the Listings ... Configuration:
Index Listing
All Listing
Featured Listing
New Listing
Then one for each of the Product Types in the Catalog ... Product Types ... Edit Layout ... and then one for the Shopping Cart in the Configuration ... Shipping/Packaging for on each Shipping modules:
Display Number of Boxes and Weight Status
Display Shipping Weight and Number of Boxes?
0= off
1= Boxes Only
2= Weight Only
3= Both Boxes and Weight
Then one for the Shipping Estimator / Shopping Cart in the Configuration ... Layout Settings:
Shopping Cart - Show Totals
Show Totals Above Shopping Cart?
0= off
1= on: Items Weight Amount
2= on: Items Weight Amount, but no weight when 0
3= on: Items Amount
I think that is all of the Settings ...