Both dahlias and Gerbera daisies need to be \"deadheaded\" or have the faded blooms removed. Just use a pair of kitchen scissors or pruners to snip off the stem and faded bloom from these plants. Follow the stem to the spot it joins the main plant to cut. The flowers fading and dying is normal but if you keep removing them you will encourage new flowers to bloom all summer. For repeat blooms you must also fertilize potted plants. If you did not use a potting soil that contained plant food make sure you add a fertilizer now. I use a slow release plant food like Osmocote around all flowering plants so that they continue to bloom until the first hard frost.