Awesome.
now on to the next thing. first a questions. how did you remove the bristle worms from the rock?
in regards to the skimmer:
turn it off for the next 48 hours. it doesn't kill bacteria but may remove it along with other solids while it's still suspended in the water column and didn't colonize the rock/glass/etc
watch your ammonia and make sure it hits 0 in the next few hours, it should by tomorrow with the bacteria added
keep an eye on nitrites, they will also start to go away. don't bother testing nitrates because nitrites are messing with your NitrAte test and showing super high, once nitrites are 0, your nitrates will test properly, if I had to guess probably 10-20ppm since you did the water change.
to answer your original questions about the skimmer. you do not need to turn it off when seeding with rock since bacteria is on the rock surface but you do when seeding with bottle since it is initially suspended in the water column before it finds home on the surfaces.
in the long run, why i said not to run skimmer at all or a while. it's up to you, that's just my method. there is not much harm to have nitrates slightly higher to prevent dinoflagellates and yes you will get some algae, it's part of a tank progress to maturity. then you can slowly start managing the nitrates and so forth. Many people run simmers right off the start but also many run in to dino problems as the result. so it's about balance and knowing that ugly stages are unavoidable but I would take ugly green over ugly/deadly dino bloom any day.
P.S. i have over 20 years of experience so I'm not just guessing in this situation if that makes you feel any better.
Edit: forgot to add that the spot on your fish may be result of ammonia burn. keep an eye on them and QT if necessary to treat with antibiotics (not in display tank)
