Colu

As more fish are developing symptoms in the main tank I would also treat the main tank

If none of the other fish in your main tank are showing symptoms then I would just treat the gourami in your hospital tank

I still think it would be worthwhile treating with Expel p once a week for 3 weeks inbetween treatments of paracleanse

It's could be a prolapse what I would do is Epsom salt baths 1 table spoon for 2 gallons for no more than 15 minutes for 5 days as Epsom salt acts as a muscle relaxant to help your fish reabsorb the prolapse @Solstice_Lacer

Looks like columnaris it's a gram negative bacterial infections that spreads more quickly at temperature over 75 and it can kill within 24hr to 7 days depending on the strain the Most effective treatment I have found is a combination of kanaplex and jungal fungus clear fizz tabs containing nitrofurazone following this treatment plan in severe cases it can take two full course of treatment back to back @trevor

I agree with @nabokovfan87 add some aquarium salt and you can add some Indian almond leaves as they have antibacterial and antifungal properties I would also add an extra air stone if their gasping @Pencapchew95

I think it's just the colour that's making it look like it's swollen I don't think you have anything to worry about if it's active and eating ok and your water parameters are fine I don't think you have anything to worry about @FyaNyan

Could be caused by injury or a growth what I would recommend is adding a small amount of aquarium salt 1 table spoon for 10 gallons at that level it won't harm your plants and add some Indian almond leaves as they have antibacterial and antifungal properties depending on the quality of the leaves you might have to add one leaf per gallon to get a beneficial effect monitor for a week after a week give us an update before then if it gets worse @ricbennett3

It's possible something else is going if it is neon tetra disease Theirs currently no treatment available for Neon tetra disease if there active and eating I would just leave them they will gradually get to the point you might have to consider euthanizing I would just keep them in quarantine and not mix them with other fish it spreads when a fish dies and is eaten that cause the other fish to become infected with to many pleistophora for their immune system to handle so they develop neon tetra disease he's some pictures of fish with Neon Tetra disease for comparison @OBXfishkeeper

What your seeing with the growths on the mouth can be a sign of neon tetra disease it can lay dormant for a long period of time before your fish start to show symptoms stress such as shipping or poor water quality can weaken your fish immune system that when you start see symptoms I would keep them in quarantine as neon tetra disease can affect angelfish danios barbs Rasboras guppies and other Tetra species @OBXfishkeeper

What are your water parameters ammonia nitrite nitrate etc how long have they had the the white fuzz as that can be a sign of columnaris it's a gram negative bacteria that spreads more quickly at temperature over 75 and kill your fish anywhere from 24hr to 7 days depending on the strain @Ohio FishPlant Dude

As you have live plants I would do the the salt baths

What I would do if you can is quarantine and treat with aquarium salt 1 table spoon for 3 gallons for a week if you don't have a quarantine tank then I would do salt baths 1 table spoon for 1 gallon for now more than 15 minutes for 5 days

Looks like the slime coat is slothing off that can be caused by flukes or bacterial infections I would recommend doing a course of kanaplex or maracyn2 they are more broad spectrum antibiotic treatments @DaniV

It's difficult to tell off your picture does it have a fuzzy appearance

Malachite green will treat the fungal infection on your Cory's it will have very little effect on columnaris

Can you post a picture of the fish and have you seen red worms protruding from the anus of your fish to confirm your dealing with camallanus worms looking at the picture the things that look like hair could be flukes or scrape marks from the skin scraping can you tell if the the marks are flush or moving with the medication you have treated with I would have expected flukes to have been dealt with if you followed though with three full courses of treatment with general cure or prazipro am not seeing anything else in these pictures that looks like a parasite @Tabeth

You could have two things going on here it could be columnaris affecting your gourami the fuzzy growth on the mouth of your Cory's is saprolegniasis it's an opportunistic fungal infection as your in Canada and your treatment options are more limited I would treat with a combination of aquarium salt 1 table spoon for 1 gallon and methylene blue I would start at 1 table spoon for 3 gallons gradually increase over the course of a day to 1 table spoon for 1 gallon just keep a close eye on your catfish as they are more sensitive to salt alternative you could contact a vet and kanamycin sulfate and nitrofurazone and treat following this treatment plan @MerrySeaMonster

Barbel erosion can be caused by rooting in sharp substrate or a bacterial infection what I would do is quarantine and do a course of maracyn update if you see no improvement after a week or it gets worse before then

I would finish the three week course of metroplex @Fishguy

Doesn't look thin he might be eating small amount of food I forgot to ask have you checked to see if his teeth are over grown that would also prevent him from eating properly

poor water quality can cause cloudy eye or it can be caused by an injury as your water parameters are fine it could have injured it's eye what I would do is add a small amount of aquarium salt 1 table spoon for 10 gallons and add some Indian almond leaves as they have antibacterial and antifungal properties if it's after a week of salt and almond leaves it's not improved then I would do a course of maracyn @asondhi

Has the puffer started to lose weight or develope a sunken belly if not it's possible it's eating small amounts of food

Your water parameters are fine what I would recommend is removing your snail if you have another tank or tote you could put it in during treatment and add aquarium salt 1 table spoon for 3 gallons that will help reduce the fluid buildup in the fluid filled sacs I would also add some Indian almond leaves as they have antibacterial and antifungal properties depending on the quality of the leaves you might have to add one leaf per gallon to get a beneficial effect and I would do a course of kanaplex

Does look like columnaris it could also have badly scraped it back on something in the tank