There were good reasons for the Tangs going, except for the Powder Blue.
Orange Shoulder Tang - Had black ick, as did all other Orange Shoulder Tangs at the LFS when I bought it. Never saw one before, so I didn't realize it wasn't part of it's color pattern, heheheh...
The Clown Tang was miniscule, very tiny, and I don't usually like super juvenile fish. Plus he was eating and acting healthy, but the tell tale sign was that he was super colored out and retained his colors well after he died, even what was left of him after the Trigger ate him (he's good at keeping the tank clean).
The Powder Blue, as I said, was weird. He was fine for over a month, and the day he died he was out swimming, eating, acting normal. Then around 4 p.m. he starts hanging out in front of the return flow current, then swims to the back of the tank and stays there. Next morning I saw the Trigger picking at his carcass.
As for the Red Sea skimmer I have the in sump. I've never had a Venturi pump so I couldn't compare but I've read that the turbo is a big improvement. Whenever mine stops making foam, I clean the inner tube as well as the collection cup, it twists and comes right out. Try that, clean all of the "black parts" of the skimmer, not just the clear tube in the collection cup. I wouldn't bother with vinegar, warm/hot water (but not too hot, it'll crack the plastic) should do the trick. I don't know what you mean by the square piece of glass, sorry.
