So I did about a 50% water change earlier and rearranged some plants/decorations in my 5gal. I also rinsed the filter pad in some of the old tank water. When I put the new water in and turned the filter back on the water turned cloudy. Is this normal? Will my Arthur be okay?
It may be the debris kicked up from rearranging the decorations- it should settle down. If it doesn't settle in 24 hrs, then I would do a 10% water only change and that should work.
If you do not vacuum/siphon the substrate regularly (if there are no live plants) then you may need to start, as it builds up and becomes dangerous for the bettas.. a filter doesn't remove waste, but just hides it.