Fish Acclimation Help

[TingeOfGinge]

I have a 29 gallon nano that currently has a firefish, 2 clowns, a bunch of inverts and both softies and LPS corals. I'm trying to add one last fish, but every time I try to add one, it dies or disappears within 24 hours of introduction. I don't know if it's something wrong with my acclimation or my tank, but since all the other fish, inverts, and corals are doing well, I'm leaning towards acclimation.
My general acclimation procedure for fish is:
15 minutes floating in the bag
20-30 minutes of drip acclimation in a bucket. At least doubling the amount of original water
Drain the bucket down the sink and catch the fish on its way out with a net
Put net immediately into the tank

And here's my fish addition history:
June 14th: Added a firefish. Still going strong, though hides frequently. Bought from LFS-1 (names changed to protect the innocent)
July 3rd: Added 2 juvenile clowns. One of them got sick in August, but has made a full recovery. Both look active and happy. Bought from LFS-2
July 12: Added a tailspot blenny. Immediately hid, but I could still see him when I went to bed that night. After that, never saw him again until his body washed up after a water change a week later. Bought from LFS-1
August 22nd: Tried again with a tailspot blenny. Immediately hid again, but saw him until I went to bed. Body found the next morning. Bought from LFS-3
September 19th: Gave up on the tailspot and got a Springeri damsel. Fed the tank after adding him and he was eating, but cautiously. Saw him again briefly 24 hours after adding him, but never saw him again. I haven't found a body, but since they're supposed to be brave and out in the open, I'm assuming it's dead. Bought from LFS-4.

Firefish is super timid and my two clowns don't seem to bother any other fish unless they get a little to close to their hosting location (which is the filter, so no other fish really go there). So I'm not thinking it has anything to do with aggression.

All of my inverts (apart from some snail deaths during a dino outbreak in late July) have been happy and same with my corals.

Any ideas what I'm doing wrong or any tips I could try? It seems like a 50% death rate is too high, and all of them have occurred in a row.

 

[TingeOfGinge]

Oh, almost forgot: the all important parameters:

Calcium: 401 (Hanna) - I have raised this recently since my IO salt was mixing low
Alk: 9.9 (Salifert)
Salinity: 1.025 (refractometer)
pH: 8.2ish (Salifert - have trouble reading this one)
Nitrate: 15 (Salifert)
Phosphate: 0.18ish (Nyos)

 

[kevgib67]

Pictures of your tank?

 

[TingeOfGinge]

Sure, here's a fresh Pic under white light

Let me know if you want something more specific

 

[kevgib67]

Sure, here's a fresh Pic under white light

Let me know if you want something more specific

Looks great! I wanted to see if you had enough rock and hiding places, I can check that off the list. #reeefsquad ?

 

[B&CinB.C.]

Have you checked the salinity of the water the fish are in when you buy them ? Quite often they will be in lower salinity .

 

[TingeOfGinge]

Have you checked the salinity of the water the fish are in when you buy them ? Quite often they will be in lower salinity .

Good point, that is something I keep intending to check but then completely forget before I throw out the water
The second blenny was apparently in water that was closer to 1.018sg (they only told me after I came back and said it died), but the other blenny and the damsel both came from tanks that shared water with coral. I never asked about them, but I'd assume it's higher