In Italian the distinction between every and any is not as clear as in English.
He can come every day.
He can come any day. Può venire ogni giorno.
The Italian sentence Può venire ogni giorno can have two different meanings. He can come every day (Monday and Tuesday and Wednesday and Thursday and Friday....) or he can come any day (Monday or Tuesday or Wednesday or Thursday ...). Nevertheless if the context doesn't allow to understand the meaning of the sentence without ambiguity you can use qualsiasi.
He can come any day.
Può venire qualsiasi giorno.
We are going to discuss qualsiasi again later.
Concerning what we said above that ogni can never stand in front of a noun in plural, there is an exception. If there is a number in front of the noun, it is possible.
evey second week
ogni seconda settimana
ogni due settimane
every third day
ogni terzo giorno
ogni tre giorni
The three pronouns which can be confused are tutti / tutte + plural, ogni + singular and qualsiasi + singular.
Qualsiasi as well as ogni can only be used together with a noun in singular.
If the arbitrariness is the main statement of the sentence qualsiasi cannot be substituted by ogni. Sometimes, depending on the context, you can use both because if everybody can do it than an arbitrary person can do it as well. But sometimes it makes a big difference and then no substitution is possible.
It didn' t make any sense what he told me.
Mi ha raccontato qualsiasi cosa.*
He told me everything.
Mi ha raccontato ogni cosa.
* In this case the arbitrariness means without sens, incoherent. It can' t be translated with an indefinite adjective to English.
It is quite clear that it makes a big difference whether he told him incoherent and strange things or everything.
He gave me to eat whatever was there.
Mi ha dato qualsiasi cosa da mangiare.
He gave me anything eatable.
Mi ha dato ogni cosa da mangiare.
I thank everybody who has given me usefull advices.
Grazie a chi mi ha dato qualsiasi utile suggerimento.
The arbitrary is more obvious when qualsiasi is postponed. In this case, there is no way to translate the sentences with a similar english construction.