If your period is really heavy and a super tampon does not hold it for more then 30 minutes should you insert another one?

After removing the first one, yes, put another one in. Never put more than one tampon in at a time. But if your flow is that heavy you should talk to a doctor. That isn't normal.

Not normal at all, if you have that much bleeding see your doctor immediately, you could be hemorrhaging.

Never use two tampons at a time. If you need to use a napkin as well. But if bleeding is this heavy you should certainly see a doctor as something is very wrong.

Only insert a fresh tampon after you've removed the first tampon, remember too that you need to alternate with pads occasionally to allow your vagina a chance to clean itself after tampon use.

You may want to consider using menstrual cups instead of tampons, a super absorbency tampon only holds up to 15ml whereas the average menstrual cup holds up to 35ml, menstrual cups don't leak like tampons, cups are safer than tampons so there's no need to alternate with pads or use pads overnight with menstrual cups, and compared to tampons menstrual cups can reduce your flow.

If you're going through a super absorbency tampon within 30 minutes then your period is heavy, although this isn't necessarily a sign of a problem you may want to talk to your doctor about checking for any potential problems and going onto medication like Tranexamic Acid to reduce flow.