Help Thought It Was Fin Rot But Maybe Not

[tha pint]

acquired a fully grown oscar , chocolate catfish and a synodontis with a new tank and after having them i noticed the oscars fins where ragged and had white blobs on them. Thought it was finrot so i treated the tank with eshas fin rot treatment. Noticed he looked a bit better so i thought that was it. just tonight i noticed some stuff which i assume was pieces of slime floating about the tank, then i noticed the catfish burying under the bogwood and noticed the stuff was coming off him. hes covered in a slimey blue coating I assume this is slime disease and ive got some aquarium salt as i hear its an all rounder for stuff like this.
what is the measurement of salt i need per uk liter . Do i treat the whole tank and then after a couple of days to a big water change.
 
btw . my tanks clean as a whistle and all my water tests seem to be all in order

 

[DerpPH]

Slime disease? Maybe its due to their skin being irritated. Their slime coat does protect them but if they are irritated, well we have problems.

I would recommend doing waterchanges a day. like 40 or something.
 
And I dont recommend salts. It can adversly affect the fish

 

[Unseen]

What are you water parameters? This is very important. Give us as much info as you can. 
 
What filter do you have? Size of the tank and the fish please. How often do you change the water? How do you do it? How do you clean the filter media?
 
When water contain toxins, white 'dust' may appear on an Oscar's slime coat. It is possibly that, but your symptoms do sound like Fin Rot as you said.
 
As for the Plec, slime disease is pretty serious. Get some Fish meds too. Try Primafix and Melafix and quarantine him of you can. I hope he survives. Could be a parasite, so check for meds for that. 
 

Bluish-white film on body, strained breathing caused by gill damage, peeling skin.

Chilodonella

Salt treatment - see below

 

[DoubleDutch]

blue slimy ? : please google Chilodonella. Ahhhh Unseen mentioned that already.It can be treated with Ich-meds as Esha Exit and Paraguard.
Esha 2000 won't do the job for finrot to my believe (though the manual says it does !!)

 

[tha pint]

Now before anyone jumps down my neck im using tetra 6 in 1 strips ( its all i can afford atm)
Nitrate 15
Nitrite 0
Hardness 16d
Kh 6d
Ph 7.2
Cl2 0

Tank is a rio 240 , filter is a well established fluval 405 , temp is 27.2 . These fish were in a rio 120 for few weeks before they where moved to the rio 240 2 weeks ago. Substrate is black aquarium gravel and sand bought from pets at home. Apart from the bog wood that was given to me with the tank and the fish there is some rocks I got with another tank about a year ago.
The week before I set up the tank I took the filter and gave the contents a wash with tank water and replaced the filter wool stuff. Left the rest in.
The day I set the big tank up on sunday and I filled the tank after adding the substrate . Added the appropriate water condition then brought the filter in and let it run for 48 hours . Brought the bog wood in and then put the fish in. Since then the next Sunday I've done aprox 50% water change
When I got the tank the oscar looked a bit ragged on his 2 front fins so I treated it in the rio120.
Last night I added esha exit and will continue with the treatment. Apart from the oscars right fin the rest looks perfect and he's eatting well and doing his thing around the tank
The synodontis seems to be his usual cheeky self , no symptoms. Catfish though is always hiding by day so he's harder to observe.
Think that covers it all . Any help?..