This material, substantially repeated in omicron 8, is taken from Procopius, Secret History 25.12. Procopius attributes the change to the emperors, rather than just Justinian. Procopius' maths is sounder than the Suda's: "thus taking off a seventh of the value of each gold nomisma from everyone."
[1] (The headword is neuter singular, the gloss neuter plural.) cf. kappa 1414.
[2] The follis was introduced in coinage reforms in around 294, and again in 494 (see phi 564 and web address 1). The solidus was the basic gold coin of the Byzantine empire between the fourth and the tenth centuries, although it is usually referred to in Greek as no/misma; stater was a more generic term for a standard gold coin, used in antiquity: see sigma 1008, sigma 1009. Procopius of course tries to stick to Classical terminology, describing folles as obols.
LSJ s.v. fo/llis gives an exchange rate of 288 folles to 1 solidus; but that was the 445 AD rate of nummus to solidus, before the 494 introduction of the follis. The exchange rate of follis to solidus went from 420:1 in 494, to 210:1 in 512, to 180:1 in 539. (Harl 1996:193).