I do not have a problem with API hardness test kit. Hardness is important to establish your tap water & conditions for the type of fish & plants you want to keep. I have found that the API color changes are easy to read & I use them all the time. I mix R/O water & you must know what your Gh is as well as Kh especially for keeping regular constant conditions . If you know what your tap water is running & it does not change much it becomes less important. However if you need say more Mg or Ca to dose than it will alter the Gh. So it is still nice to know what the Gh is at any time you want. If you decide to mix r/o water for what ever reason than you will need one.