Windshield that won’t clean

[Punkindave]

Vinegar or CLR if it's calcium

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[ormandj]

I see the OP removed it with vinegar, which indicates it's just hard water. Test your water post-softener, it sounds like it's not at 0 gpg of hardness.

For others who are this and it's not easily removed with acids like vinegar, it may be silica, I have a softener plumbed to an outdoor faucet but due to silica content in my water I get extremely stubborn spots like this if I don't wash in the shade and dry immediately.

Here's the bad news if it is silica - it is far more stubborn than normal hard water stains, and needs mechanical removal with a glass polish and rotary tool. I have to do this with my shower doors from time to time, and I have 0 gpg of hardness and use a squeegee. RO is the only thing you can do to prevent this.