On the second row, he used 9 - 2 = <<9-2=7>>7 blocks.
On the third row, he used 7 - 2 = <<7-2=5>>5 blocks.
On the fourth row, he used 5 - 2 = <<5-2=3>>3 blocks.
On the fifth row, he used 3 - 2 = <<3-2=1>>1 block.
Therefore, he used a total of 9 + 7 + 5 + 3 + 1 = <<9+7+5+3+1=25>>25 blocks.
#### 25