Unless you are taking a cheap instant screen only with no type of validity check whatsoever, Do not use Quick Fix 3.0! Spectrum Labs has recalled the 3.0 in Dec 2003, replacing with the 4.0 formula. If you still have 3.0, Spectrum can swap it out for the current formula FOC.

On Feb 2008, Spectrum has extended the recall to QF 4.0 with batch numbers ending in 03 thru 05. These were early 4.0 batches made between 2003 to 2005, but a suprising amount of these batches are still in circulation. If your 4.0 carries these batch numbers, Spectrum can also swap these out.
Later QF 4.0s with batch numbers ending in 06 and later are still good at this time.
Spectrum still hasnt officially included the QF 4.2 on their online product list. But Ive noticed detoxforless website recently began advertising the 4.2.
Burnt Toast Reviewed by Burnt Toast on . QF 4.0 vs. 4.2? Temperature strip accuracy? Hello, my name is Steve, and this is my first post after several months of "lurking". I've looked through the substitution sticky and I appreciate all the advice that everyone has posted. I have a test coming up, and a few months ago I purchased some QuickFix 4.0. I've noticed that there is now a 4.2, and I have seen people recommend switching to 4.0 if they have 3.0, but not so much about the difference between 4.0 and 4.2. The only thing I could really find is that 4.2 is less proven than Rating: 5