It is possible your router changed the IP address, they can do that sometimes. To stop that you have to set it as a static IP address in your router settings. The findmyip site will show you the IP address from your internet provider, you can't access reef-pi using that without setting it up and it's not safe anyways. Typically local network IP's will start with 192.168.xxx.x.
Another option is to assign a hostname to the Pi, that should always work. You can set that using the SSH terminal with the following command.
sudo raspi-config
That'll open a menu, select the first option "System Options" and then go down to "Hostname", set that and when you exit it should ask you to reboot. Then you can use that in your brower like this,
http://hostname