Help with multi-problems

Help. I have too many things going on with my Saltwater tank. In the medical world we always say if there is one problem, look for another. I am beginning to think the Aquatic World might be the same...
So within a few hours time I noticed what I believe to be Ich on a couple of fish, then my Xenia tanked and I think I may also have a fish with Marine Velvet Disease. Never mind the fact that I have a coral beauty that has gone missing for the last six days! I have attached photos, in hope that someone will be able to assist me and my fish Thanks!!

 

Can we save them?

Brief description of the problem. See photos and description up above, but here is more information.
A picture(s) will also help. (see prior post)
PARAMETERS (important)
Temperature: 78-79
PH: 8.2-8.3
Ammonia: 0
Nitrite: 0
Nitrate: Currently between 25-50. Test is hard to read.
Salinity: 1.23
dKH/KH/Alkalinity: In target
Magnesium: Unknown
Calcium: Unknown
Phosphate: In target
Test kits you own: Saltwater Master and many others
Liquid or Strips: Both
Brand Name:
Are they Expired?: No

Tank size? 55
Estimated total system? 60
Reef, fish only or, freshwater? reef
Current inhabitants? What and how many? 1 small black clown, 1 small burgundy clown, 2 false ps, small blue tang, med purple tang, small mandrin goby, currently missing coral beauty

Soft corals, mushrooms, polyps, xenia, trumpet coral, brain coral.

Clean up crew? 1 peppermint, 2 cleaner shrimp, 1 fire shrimp, numerous emerald crabs, 1 sandsifter star, numerous hermits and a couple snails
How long has your tank been set-up? 2 years
Substrate. live sand
Type?
Depth? 2-3 inches depending
Live rock? yes
How much? 60 lbs
Did you recently add some? yes. Added 2 purple tipped hairy mushrooms on a live rock
Filtration. wet/dry
Type? 100 gal
Protein skimmer? yes
Do you wet or dry skim? I guess I dont know. I have a protein skimmer that sits next to my wet dry system in the area that collects water after it flows through the bio balls.
Maintenance schedule for filtration? alternating filters every month
Drilled tank/hang on back overflow? yes
Sump/refugium. What's in it and how much? 3 gallons
Macro? What kind?
Lighting. Multiple on timer
Lighting type?
Age of bulbs? 2 years
Feeding
What? spyro, krill, myosis shrimp, seaweed (variety on diff days), plankton
How much? (2 frozen cubes)
How often? 1x per day
Water change schedule.
How much? 20 gal
How often? every other week. Just had multiple changes over several days due to spike in nitrates into danger zone (100 range easy). It was dark and frightening. Suspect it might have been related to several things: Potential rotting dead coral beauty, xenia crash which might have all been precipitated by bizarre skimmer incident that I cannot explain. Came into room. Saw a large amount of sediment shooting out of pump directly into tank. Opened cabinet and saw massive amounts of foam coming out of skimmer, over top and into pump catch. Almost like skimmer was turned up full blast. But, it was not. Even keeping skimmer on lowest setting resulted in massive amount of foam. I had to turn it off completely for a couple hours while the foam settled.
What salt brand? High quality, cannot recall name
Water source? treated tap, but used specialty treated water from saltwater store after the "skimmer incident"
Additives/supplements used? Iodine, Reef Vital, marine alk buffer, now using marine max and garlic for suspected parasites
Do you have a ground probe? No
What kind of flow does your tank have? medium current

 

you need to find and remove the dead coral beauty from your tank and do several significant water changes to try to salvage your xenia. the cb probably died first from whatever parasite your fish are suffering from. others here will be able to give you advice for your surviving fish.

 

it really would be good if you could start a new thread. this thread was originally made to explain that to people..copy your info from below and paste it into a new thread in the asap category....... you will get more answers if you do