Need some help with my skimmer.. pics

[One_Divided]

I looked at the general specs on the precision marine page when I made my skimmer.. Not that I disagree (I know next to nothing on building skimmers), but if the precision marine airstone model works; why not go 18"? Obviously longer contact time will be better, but damn acryilic tubing is expensive! lol.. I would think that the small bubbles produced from the airstones would make up for that to some degree with more surface area.

Look at the specs here