Ive been doing a bit of saltwater keeping in my time, and what I know about PS is this.
What it sounds like one would use is the air stone one ( the wooden block) What it does is it has very, very small holes and what happens when its in the water, the bubbles are so fine that it is able to "capture" the fatty oils (the mucus or oil on a
SW tank) and bring it up to the top, breaking it down to what one sees as while bubbles. Its kinds similar to a jacuzzi filter in a way that if you dont clean the water after time, the oil from peoples skins create a yucky ring on the side and the bubbling from the jets create that oily bubbles.
The airstones run at 3$ at almost any
LFS. Im sure ill try it on my new discus setup.
You can make you own PS with some
PVC pipe, that airstone and air tubing and air pump and a
PH to circulate the water. I made a 3ft one for my 150gal and even though I was over doing it a tad, I never had a problem. I dont see what salt would make a huge difference. Ill try it in the next few days simply by putting oil to a cup with my tank water and hooking up one of my spare airstones and see if I get anything.
Hopefully I explained something, and hopefully im right
Ill let you know in a few days to see what I got. (My jacuzzi example involved no salt.....)