Weight and Dilution

Hello all....

I'm new here and have spent a LOT of time reading about the in's and out's of diluting. I have a test coming up Tuesday where subbing isn't possible and I think there could be a risk for testing for additives. So now I have a question regarding dilution and hope someone will be able to help me.

First....a little background. Up UNTIL a week ago I was a daily user for YEARS of a few hits right before bedtime. I weigh 115 lbs and since I always had problems gaining weight I never bother about excercising UNTIL about a couple of weeks ago. I think my body fat is around 23 percent. I have bought test strips and did prelimary test runs. A few days ago I tested after diluting (initial 48oz with additional water at the rate I voided) and came back positive (VERY, very, very faint line...almost ghost-like). BUT...after thinking...I tested right after excercising the evening before...so that may be why it came up positive. Tonight...just for kicks...and without excercising or diluting...it came up POSITIVE...no ghost line at all. I can't help but wonder if the first test was on the verge of a negative with a ghost line.

Now for my question....does it take the same amount of water to properly dilute ones system regardless of your weight? Also...if my test is Tuesday what day should I STOP excercising?