Minimum balance for ALGO
ALGO is a special asset that requires an address to have a minimum balance. That amount is at least 0.1 ALGO.
If you try to make a transaction without taking the minimum balance into account, the transaction will fail. In other words, if you have 0.5 ALGO and try to send out 0.5 ALGO, the transaction will not go through (since sending out 0.5 ALGO will put your balance below the required amount of 0.1 ALGO).
For that reason, Atomic Wallet locks 0.1 ALGO on your balance so that the address could stay activated and ready to use. Thus, 0.1 ALGO is always excluded from your available ALGO balance.