I've never seen 30mg ephedrine tabs. If you are in the US, the max legal dosage they can manufacture is 25mg. There are some states that can only sell 12.5mg tabs.
That being said, you don't want to go over 25mg at a time. I take 25mg either twice or three times a day, depending on if I can tolerate the 3rd dose... Some days I can, some days I can't.
The only light I can shed is that 75mg/day should be your max dose to remain safe. I've seen people go higher, but you really are asking for problems if you go over 75mg/day