I agree the stock list was a little high on bio-load, I figured the 20g sump/refugium would be able to handle the nitrates and skimming would take care of the rest, but I was prepared to move the GSP to another setup if he got too aggressive anyway so if my parameters got unmanageable I would have just setup the other tank.
As for my live stock, they died 1 by 1 last night, I set up a 10g that I have divided in half and all I have left is my occy (still doesnt look good) and snowflake(look OK but not entirely himself)... All inverts are still fine, corals are upset they have been moved but are opening slowly. I did notice that my urchin started dropping spines yesterday, but I don't know what that is a sign of.
Basically I'm tearing my tank and refugium down and starting from scratch, I don't know what caused it so I'll soak all my LR
in case there is a chemical that got in to the water and soaked in to them, get rid off all the sand, scrub all equipment with water and maybe vinegar if needed. Replace all of the sand in the fuge, fill her up like new and try again.