The API strips only go as high as 180 ppm so your GH could be 180 or anything higher. Can I suggest you look at your water company's website for hardness. It's usually on a page called in your area or something similar. Most have a box to enter your address or postcode. Make a not of the number and the unit of measurement as there are several they could use - or better still, post a screenshot. If you can't find it, tell us the name of the website and we'll see what we can find.
It is better to get fish which need the same hardness as our tap water. Altering the hardness is not something to be undertaken lightly. With 64 litres (17 gallons for our American members) toy do need to choose small fish. Fish such as endlers or guppies, though males only as females have a lot of fry and would overpopulate the tank very quickly; or some of the smaller rainbowfish in the genus Pseudomugil https://www.seriouslyfish.com/species/search/pseudomugil
But we do need to know how hard your water actually is before suggesting fish.
It is better to get fish which need the same hardness as our tap water. Altering the hardness is not something to be undertaken lightly. With 64 litres (17 gallons for our American members) toy do need to choose small fish. Fish such as endlers or guppies, though males only as females have a lot of fry and would overpopulate the tank very quickly; or some of the smaller rainbowfish in the genus Pseudomugil https://www.seriouslyfish.com/species/search/pseudomugil
But we do need to know how hard your water actually is before suggesting fish.