If you're trying to update the firmware on your PoolLab photometer and it gets stuck (usually on 5% or 7%) there are several things you can try to solve the problem.
The easiest is to try the update with another phone or tablet, preferably one with Bluetooth 4.2.
If you don't have another phone you can follow these steps:
If you're using an android device make sure smart lock is disabled (Settings -> Security -> Trust agents)
Close the PoolLab app completely
Ensure your phone has the latest version of the PoolLab app
If the PoolLab shows "BOOTLOADER ----- Waiting for update ..." press the pH button for 2 seconds and the device will restart
If the PoolLab is paired in your devices bluetooth settings, unpair it
Turn off bluetooth on your phone, wait 10 seconds and then turn it back on
Start the PoolLab app
Reconnect with bluetooth in the PoolLab app
If the phone asks to pair with the device select "Yes"
Start the update again
If the update does not finish again try these steps:
Close the PoolLab app completely
On the PoolLab press and hold "pH", "fCl", "TA" and "CYA" buttons and release them simultaniously after 1 second
Turn off bluetooth on your phone, wait 10 seconds and then turn it back on
Reopen the PoolLab app
Connect to the PoolLab, which should now identify as "PoolLab OTA"
Start the update
If this doesn't fix the problem repeat the steps again as it may take several tries to complete.