You really need a picture. There are several parasite diseases that can cause fish to twitch or flash. Also, depending on the species of cardinal involved, the spots may be natural.
With ich look for small spots that also seem to be a bump and are in places you would not expect to see spots like this, like fins and on the sides.
If the spots look like fine gold dust, you may be dealing with Oodinium. Sometimes it's called gold dust disease because of the way it looks. Treatment for this is by copper. Note - Hyposalinity does not work for Oodinium.