dont forget the Dat too in that list......
its no doubt that you have a great collection of fish but seriously they are not a good combination to keep together.
firstly the lobster if given the chance will attack the fish when they rest at night so its not a good idea to keep lobsters and fish together. i think the same will apply to the turtle, they have strong mouths that will shred a fish.
the catfish which looks like a pangasius will get huge and need a massive tank, way bigger than you can imagine... the angels and discus are fine together as long as the angels give the discus chance to eat, this is normally the main concern of adding these 2 species together but in this tank with the species kept thats really the last thing to worry about... also discus prefer high temps of about 30 degrees C which many of the other fish you have will not feel comfortable im affraid
the panaque pleco will also get huge, ive seen one at about 16 inches before but this wont happen quickly so not to worry too much although they do need wood in their diet and given wood they will eat and eat and eat leaving a huge mess behind

i had one that was about 7 inches and it covered the substrate of a 6.5x2x2 tank overnight!!!!!
the spotted perch are a cool fish but predatory. the fish in the tank will be ok as they arent too small to be seen as food.
to be safe i would rehome the turtle and lobster straight away along with the pangasius because when he starts growing everything in that tank will be lunch... then think about what fish from the remaining you prefer. if its discus then i would settle with them and the angel and maybe add a few more and some dithers such as cardinal or rummynose tetras which can handle the higher temperatures needed. as this started off about the panaque slime eating then im affraid he will have to go too. take him to an lfs and explain the situation tell them to keep it with other plecs or as a singleton and see if they can find a plec fanatic who can add it to a group. then theres the dat.... these get huge and arent an easy fish to keep so this will have to be moved on at sometime so if you decide to take some advice then this is the best time to do it
as i said you do have a great collection of stunning species but they just wont get along as soon as they need their own space and territories. i fear the discus wont get enough food as they are slow grazers and are in among some greedy and fast eating fish. that along with the temperature of the tank wont suit them at all. personally i would just keep the angels and discus and maybe the perch although keeping this fish will limit your stocking if you wish to add tetras or smaller dithers to make the discus feel more secure. up the temp to 30 degrees and if the tanks big enough add a few more discus as they do prefer to be in groups, the more the merrier depending on space that is.
its your tank and they are your fish but you did come here with a concerning matter. this can be resolved by removing just 1 fish but i think that your problems will only get worse as these fish grow a bit. if you take the advice or not please keep us up to date with the tank and fish as they are some stunning fish you have.