The GH of my tap water is 21

I tested my shrimp tank and GH is 21- tested my tap water hoping it was just accumulation of minerals but nope, it’s also 21. KH is 6.

Ammonia is 0, nitrite is 0 and nitrate is in the 20 range, to be thorough. All API drop tests.

I’m not planning to get a RO system. I got some distilled water and did a 10% water change. Planning to continue doing distilled 10% changes until GH is down to.. what?

And then for future water changes, should I mix 50/50 tap and distilled?

One of my wild types who’s been saddled for weeks for photo attention.