How to use other cloud for iPhone & iPad instead of iCloud

Very complex, as Apple is after your data. The more data you store with them, the more likely you are to use iOS products forever.

To do what you're asking, you'll...

1) Determine what private cloud you'll be using.

2) Then use their cloud access App. https://support.invisionapp.com/hc/en-us/articles/211880746-Accessing-a-Private-Cloud-instance-via-the-InVision-iOS-App provides one example.

3) If you're setting up your own private cloud or using a cloud with no iOS App, you'll have to write an App.

4) You might research https://github.com/owncloud/ios as a way to access your own private cloud data. You'll have to setup your own OwnCloud instance or purchase access to an existing instance.

If you wish to use a Cloud for your Apple devices, use iCloud.  Too difficult otherwise - I agree with David above.

If you wish to minimize use of the iCloud, keep pictures and music on your computer by iTunes and copying pictures from iCloud to your computer and deleting on iCloud. Even this takes some management.

As John suggested using iCloud is normally a binary option. Either use it or not.

For me personally, I avoid using iCloud 100% because I'd rather keep all my data private.

If you opt for any other company run cloud, then there's no difference between using Apple's cloud + someone else's cloud.

The only real boost in security is if you setup + run your own private cloud, where you + only you have access to your data.

Maybe some info: I just activated free 50 gb cloud with mega and wanted to have the backups like whatapps and other iphone apps to be done in mega instead of icloud... how can i do this?

The way I do this is log into iCloud, go to the section, download what I want (photos in my case) and once secure on my computer, I delete from iCloud.    

As we have both pointed out here, there is no other Cloud media to do this.  IOS only looks to iCloud.

Seems complicated, but will work with this option.  Thanx