Ever since I have heard about pHin and other "smart" testers I have been warning people against them. Simply put, they do very little to justify their cost.
The actual pHin unit has 3 sensors: a thermometer, an ORP sensor to measure chlorine, and a pH sensor. Unfortunately one big issue with ORP sensors is that they lose a lot of accuracy as the CYA level increases. Even going above 30 can start to cause erroneous readings. With that sensor being untrustworthy you are left with a thermometer and pH sensor. Figure out the price of a digital thermometer and pH meter and you will see why pHin is not a very good value.
Now, consider the competition. If you pop in to Walmart you can find a set of Clorox test strips that you scan with a smart phone and it reads the strips and inputs the values in to an app which tells you what to add to your pool. Pretty much what pHin does. $7.00 Only seven dollars for virtually the same thing. Nothing pHin adds is worth the price they charge for it.
However, we still do not recommend either. Why? Test strips are notoriously unreliable. We have seen several times where someone will dip two strips from the same jar and get different readings on both of them. People with fresh fills have reported a CYA level of 50 when there is no CYA in any water supplies in the US. They are invalidated when chlorine levels are a bit elevated, they are ruined if moisture gets to them, and with the manufacturers competing to keep price down the quality is just abysmal.
When we try to help someone with their water chemistry we know that accurate and reliable numbers are the foundation to that. We take water testing very seriously here, it is the only way to know you are doing it right. It is the reason most of us rarely see a single speck of green in our pools. That and recognizing the effect CYA has on chlorine and adjusting accordingly, a relationship discovered 40 years ago yet the industry is only just starting to take the smallest of baby steps towards implementing.
But anyway, I wish you luck with your pool. Hopefully a fresh fill will do the trick for you and you can get back to enjoying it. If you need any help you know where to find us and what information we will need to be of assistance.