Help with DDR volume tracking

[Struttmaster]

Hi, I am using a DOS/DDR combo to dose phytoplankton. The DOS is programmed to run in reverse prior to feeding to agitate the phyto and again to clear the lines following feeding.
I am trying to track volume in my DDR but it thinks I am adding fluid when the DOS is running in reverse.
Can someone point me in the right direction so my DDR ignores volume change when my DOS is running in reverse?
Many thanks

 

[blaxsun]

@SuncrestReef