Hi. Obviously your nitrates are too high, any colour going into the red zone is bad. However, if you really want to know the reading you can mix tank and tap 50/50, test it and double the result.
Sent from my iPad in West Yorkshire, U.K.
Once you get below 40 you can easily judge how much water to change to reach your goal. I keep my tank between 10 and 20, below 10 is too much hard work although it drops considerably when I'm away and the tank is on minimum feeding.
Sent from my iPad in West Yorkshire, U.K.