Questions - Need some input

Ok so just a few quick questions as this is my first skimmer.

1. Are skimmers in general meant to always have the foam at the top of the neck or just when there is something to skim? For example when you clean green algae off your glass.
2. Does it matter how deep in the water they sit or is it just a matter of adjusting them to your desired skim rate?
3. Is it better to see large/med bubbles coming out or small bubbles like a frothy foam?

Here are some pics ...

Hey all i came down stairs to feed the fish this morning and this is what i found.

I am not sure what was going on (i am referring to the strings coming from the center/mouth) so i grabbed the camera to show you guys and ask the question. Then this afternoon i found this.

Almost looked as if it was puking its guts out literally. Moments later it looks like this.

I had forgot ...

Ok so it’s been a little over a month since my last update so I thought I would post an update on how things are going and to get some suggestions. First let’s start with some before and after photos.
Tank early December

Tank now


Pulsing Xenia December

Pulsing Xenia Now

Green Button polyps December
...

Hey All
I am starting to put together a plan for my next step which will be a sump and skimmer and would appreciate any input you might have. For those of you who did not see my other posts i have converted my 108gal fresh water tank to salt water. It is going decent so far and i will try to do a tank update soon.

First off as for a sump i was thinking of building one based off of Marcs' website but when i called about acrylic my local supplier only carried the brands Plexi ...