Learn English – Plural of “uh-oh” and “oh-no”

The entry for flux in the Oxford dictionaries does not show any use of flux in plural. It actually annotates some of the uses as mass nouns.

However, the plural form fluxes is often found in technical texts. Here's a quote from a very well-known text-book on Physics:

"If we now add Eqs. (3.14) and (3.15), we see that the sum of the fluxes through S1 and S2 is just the sum of two integrals which, taken together, give the flux through the original surface S=Sa+Sb." (The Feynman Lectures on Physics, Volume II)

If you still prefer to avoid the use of the plural form fluxes, you could do so by replacing the sum of fluxes with the total flux.

EDIT

With @alex_reader's help, I've found that the oldest occurrence of fluxes linked by Google's n-gram viewer is:

"There are some which become tarnished by fluxes, that contain the oxydes of lead." (The circle of the mechanical arts -- Thomas Martin, 1813)

Merriam-Webster's Eleventh Collegiate Dictionary (2003) suggests that the original apocalypse wasn't conceived of as a one-time-only armageddon:

apocalypse n [ME revelation, Revelation, fr. AF apocalipse, fr. LL apocalypsis, fr. Gr apokalypsis, fr. apokalyptein to uncover, fr. apo- + kalyptein to cover — more at HELL] (13c) 1 a : one of the Jewish and Christian writings of 200 B.C. to A.D. 150 marked by pseudonymity, symbolic imagery, and the expectation of an imminent cosmic cataclysm in which God destroys the ruling powers of evil and raise the righteous to life in messianic kingdom b cap : REVELATION 3 ["cap : an apocalyptic writing addressed to early Christians of Asia Minor and included as a book in the New Testament — called also Apocalypse"] 2 a : something viewed as a prophetic revelation b : ARMAGEDDON ["1 a : the site or time of a final or conclusive battle between the forces of good and evil b : the battle taking place at Armageddon 2 : a usu. vast decisive conflict or confrontation"] 3 : a great disaster {an environmental apocalypse}

While definitions 1b and (for the most part) 2b refer to Apocalypse as a one-off event, definitions 1a, 2a, and 3 do not. Perhaps most interesting, definition 1a suggests that someone living 2,000 years ago could make a career—or at least an avocation—of writing apocalypses.

The prospect of multiple apocalypses in the definition 3 sense is bolstered by the history of film over the past fifty years, wherein the possibility (if not probability) of countless zombie apocalypses—especially in Hollywood—has become an industry trope.

As for the plural form, it is simply apocalypses, just as the plural of eclipse (which has a different etymology) is eclipses.