Chaque matin, je vais à la piscine.

Hi Mark,

Yes indeed, you could  say:

Le matin, je vais à la piscine

But it means -

In the morning I go swimming ( not in the afternoon or the evening)

I have been informed that what they were looking for was the frequency not the time of day for swimming which could only be -

Chaque/tous les 

Hope this helps!

Hi Chris, 

If this refers to a Quiz, you need to contact us via the 'Report It' button on your correction board as it will link directly to that quiz.

But I suspect that, although both are correct,  it depends on what is being tested ...