CUC is about 20 hermits 25ish snails 2 conch and a brittle star. I have a 36 wt uv sterilizer that I'm running about 400 gph through and lastly I have a bag w carbon and gfo mixed in the last chamber between the fuge and return pump.
When you say stop everything but skimming and water changes do you mean socks and the fuge also?
The rock came out of the old tank directly to the new one.
CUC
That's not a lot for a 180, but you do have to judge the correct number by the amount of algae available. Just be aware that there should be plenty of room to increase those numbers. Personally I'd never have more than a handful of hermits in the tank. So I'd also let the population shift to snails over time. Not sure if you'll have luck with the conchs....that's probably too much snail for that tank. One might even be a lot. Stick with Ceriths and Turbo's (e.g. turbo, trochus, crown top...even asreas).
UV is likely to be suppressing the dino's, and carbon could be eliminating most of the toxins, if any are being formed. Good for the tank, but might make the symptoms harder to see.
A Few More Questions
What is your UV set up to target at that flow rate? Dino's are armored and it's thought to take a high-power dose to kill. (Sensible, but I still haven't seen any lit. on this however.)
Any strange behavior by the CUC like seeming to be stunned or drunk and slow-moving?
How about micro-CUC? How are your pods? Less than normal? Slower than normal? Mostly standing still instead of finding and eating food?
Recommendations so far
Like @sfin52 said, I would definitely cut off the GFO.
If you have a ton of algae in the fuge I would probably at least remove a good percentage of it – 75-90%.
I'd probably remove all of the algae if you will not have a problem replacing it later on.
If you're on a monthly carbon-replacement schedule (for example), reset the clock now and clean out the bag. Reload it with 1/4 the amount of carbon (only). Replace it weekly. Do this at least until you're able to rule out dino's.
And watch out for that brittle star....if motivated they are excellent fish and crustacean hunters. Ambush style at night, while the target is sleeping (fish) or exploring (invert). Plenty of folks have lost fish and mine ate a porcelain crab that was almost as big as he was. Didn't see it happen, but I know the star's body wasn't crab-shaped when I left him and the crab was never seen again. The "swallowing" must've been a real sight.