3 x 6 min with Level Change 
Vary stroke rate as follows per interval: 

First and second intervals: 
2 minutes @ r20
1 minute @ r24
2 minutes @ r22
1 minute @ r26

Third interval: 
1 minute @ r20
2 minutes @ r24
1 minute @ r22
2 minutes @ r26

Let the rate control your speed while staying consistent with each interval. Kept the pace moderate while staying focused on clean technique.