Is he resting on the filter? Pretty typical behaviour. If he doesnt have some quite place to rest (on plants or decor) thats the cause. They tend to go thru patrolling around, then lazing on something for a while (in this case the filter) and then go back out for patrol.
So long as he is able to swim around without struggling and the filter current isnt blasting him around the tank, the filter is fine (you could always dampen the outflow tho if it is too strong). Get more resting places for the tank. A few of my guys love to squeeze behind their heaters for rest, even though they have plenty of choices for other places to be lazy.
All the best
Cheers