I dont know what "the age of the pisces" means ect.. Ive never poked into that sort of knowing... I also dont know what miasmas is...
The age of the pisces refers to the great year. Our solar system is doing a kind of circular movement just like the planets move in circles. This Solar circle is about 25 000 years and astrologers divide that part into 12 pieces, one for each sign. Now the only difference from the normal year is that the Great year is moving backward in the Zodiac. So before the age of the Pisces there were the age of Aries.
It is usually said that the age of the Pisces started about the time for the birth of Christ. There is a book about these ages written by Zipporah Pottenger Dobyns; The Zodiac as a key to history. Tia Publications. Los Angeles. 1977.
Miasma is what caused a disease before man knew about bacteria, virus and the direct health effects of public nuisance. Miasma was said to exist in certain areas if people was found to get sick in certain diseases, especially when epedemies occured. I suppose you can use the word "miasma" for any poisened or negative thing as well.