YOU SAID:
I am so tired when I walked to the pool
INTO JAPANESE
プールに歩いたときはとても疲れました
BACK INTO ENGLISH
I was very tired when I walked to the pool
INTO JAPANESE
プールまで歩いたときはとても疲れました
BACK INTO ENGLISH
I was very tired when I walked to the pool
That didn't even make that much sense in English.