All players receive only one Arena daily reward based on their highest rank in the two Arenas.
To receive the daily reward for your Arena ranking, you need to attack at least once in Arena or Grand Arena before 8:00 PM, your in-game time zone. You can check the time zone by tapping your avatar in the upper-left corner. Note that successful defenses are not taken into account when issuing the reward.
Besides, you receive 10 Arena Coins only for the first five successful defenses, up to 50 Coins per day. All further defenses are not rewarded. The Coins arrive in a letter in your in-game mailbox.
The same rule works for Grand Arena. Thus, each day you can receive up to 50 Arena Coins and 50 Grand Arena Coins for successful defenses.