3 fancies, 3 different symptoms to 1 affliction?

Ok so I have 1 black moor, 1 oranda and 1 pearl scale.
They are in a 30 g for now, in January they will get a 55 or more as there X-mas present
I do 30 to 50 % water changes weekly.
Filtration is Eheim 2213. It is too small for the job but for now it is what I have. (would be fine with tropicals in a 30G but not messy poop-king goldies lol).
Air is tetra whisper 60 at about 55% flow.
Only food fed to present is New Life Spectrum goldfish formula.
Light is on for 8 hours per day.
Decorations are rocks: natural and acrylic coated. Plants artificial silk plants (from china with cement like base). Substrate is lfs purchased small river stones, 1 moss ball and african root wood.
Everything added to the tank was boiled or well cleaned.


Water parameters are:
ammonia= 0
nitrite= less than .1 ppm
nitrate= less than 5 ppm
PH= 7.4 to 7.6

Now to the story...

Last Sunday (water change day) I didn't do a water change I did a full filter cleaning. It was nasty! The bottom was full of long chords of goldie poop!
Anyways since I cleaned the filter I decided not to do the water change.

Then Monday while talking to a friend about the poop! She strongly suggested I use 'waste control' as she uses turtle waste control for her pond and it works...
So I got a bottle of nutrafin waste control and added the recommended amount.
From there my water was cloudy.
I attributed it to the waste control alone but now I wonder.
Now as the week rolls on the tank seems to remain somewhat cloudy but clean.
The fish were remaining active, hungry and mobile.
Then yesterday I noticed all three in the bottom third of the aquarium more then usual.
I was on my way out but told myself I better get a water change in tomorrow!

So today when lights come on, cover off!
The Oranda has 3 white spots on his head.
The black moor looks like he ran through a bakery, a white dusting on him.
The pearl scale has 2 red strips along either side!
I thought ammonia burn!!
So the good boy scout that I am I did a 50% water change on the fly!
Oops should have tested the water first!!
Well so the parameters above are from right after water change and 1 hour later matching results.

So please tell me by your experience what I am dealing with and how to handle it.
Sorry the pics aren't the best, I spend all my loose cash on fish nothing left for a better camera lol :dance2:

Going to do another 50% water change in the morning.

well ........ Bump
hoped for more responses on this. I have very little experience with goldfish and most think they are simple low maintenance fish but they have their issues still.
Hope to wake up to some ideas.

I just rinsed the poop out of the canister and rinsed the media briefly.
I think it is ammonia burn and in consequence has caused bacterial infections.
I have started a maracyn treatment. I guess I shouldn't do any water changes while treating right?
Any other tips?

Tap but I treated the water I put into the filter before reinstalling it.
Same as when I do a water change with my siphon it is straight tap water that goes back into the tank but I condition the water.

I rinsed with tap water then filled with treated water.
I heard that about the antibiotics but there is only those three fish in there and they all have symptoms.
I was thinking after the treatment I would do a few days of water changes and then add seachem stability.
Is this a good way to go about it?