Do I need more flower food for my flowers?
The companies that manufacture commercial flower food know that the only hands on time most consumers spend with their cut flowers is when they're putting them in a vase for the first time. That means no vase water changes, no stem trims, etc.
Accordingly, commercial flower food is generally designed to be a one and done solution, coming with enough food to sustain cut flowers a few days longer than they would have lived without any additions to the vase/additional water changes (assuming they're also kept away from direct sources of light or heat, of course).
All that said, if you see something,do something. If the vase water is looking cloudy or gunky, gently remove your bouquet and place it in a temporary vessel, like a drinking glass, to maintain its shape. Empty the water from your vase and give it a quick clean with some soap and warm water. Refill your vase and replace the flowers. Repeat as often as you can remember and, if you're really going for gold, every day.
This is also a good rule of thumb for any flowers you bring home that don't come with flower food.Fresh water is the single best thing you can give you stems to ensure the longest vase life.