Crystal Light and diet sodas have Aspartame in them, which is a big NO NO.
Stick to either water or dilute store bought juices. Look for juices that are NOT from concentrate.
As far as weight loss, I just complete day 5 of my Water Fast and have lost 8 lbs and my clothes are a lot looser. I started at 183 and now I am 174.6. Not too bad for 5 days.