Something to keep in mind Mike is that sinking tubing, depending on how much you have to run, can often be more expensive than the diffusers themselves.
You don't have to run sinking tubing. You can use some cheaper tubing and use makeshift means to sink it (it will float". But if you try this you will only do it once. The sinking tubing made for the job works Sooooo much better the second time you will spring for the sinking tubing so might as well save the effort and buy it to begin with.
