Are you testing the coolant because it was contaminated or diluted sometime in the past? A good rule here is 5 years of use with G48 and G05 Zerex stuff. Just drain and replace if the liquid was a 50% mixture. The additives get depleted by then.

If the liquid was not a 50% mix, you will need to do some math to correct that mix.

Now if you were using something like a Peak's Final charge or any ELC your 5 year mark doesnt count, that coolant can work for upto 10 years in these cars. And to keep in good condition, you can buy the test strips for that specific coolant.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)