do a large water change (80%) and up the temp in the tank to 30 C (86 F) if possible...remove any carbon from the filter (the black stuff)...increase aeration to the tank (either add an airstone if you dont have one already or if you have a hang on back style filter lower hte water level in the tank a bit so it splashes more). add a whitespot(aka Ich) med and dose the tank as per directions on the package.
agreed to not use copper if you have sensitive tankmates like inverts (copper wont kill live plants...seems to be confusion on that)...half dose for fish like cories, plecs, tetras if you have thses guys in with your betta. continue treating for a full two weeks after the spots have gone!!!
good you noticed, luckily whitespot is easily treated when noticed quickly and the fish usually make it!
best of luck and any other questions feel free to ask.
cheers!