Colu

It looks like a fluid filled sac the constant flaring is probably tearing fins that why your not seeing much improvement what I would black out the side's and back of the tank and add some floating plants to help reduce reflection that could be causing him to flair also what are your water parameters and what medication have you treated with as most cases of fin rot are caused by gram negative bacteria @Confetto

It's not looking good all you can do at this point is give the medication a chance to work I would up the level of aquarium to salt 1 table spoon for 3 gallons he might be to weak to recover@MattyM

I have used kanaplex in my planted tank with no problems

Indian almond leaves are really beneficial for bettas as they have antibacterial and antifungal properties as @xXInkedPhoenixXsuggested also have you seen him nipping his own fins that is common in long fined bettas if he's flaring a lot that can stop the fins from healing if that the case you want to add things to try and distract him like adding some floating plants add a background to the tank to cut down on reflections as he might be flaring at his own reflection add a floating log as @xXInkedPhoenixXsuggest add some some more plants I would also add some aquarium salt 1 table spoon for 5 gallons at that level it won't harm your plants if after a week you notice the fins getting worse then I would do a course of kanaplex it a more broad spectrum antibiotic treatment@alcidmr

If it I would treat all your fish What I would do is start treating with paracleanse instead of prazipro as you have it to hand if you can get levamisole that the active ingredient in Fritz Expel p I would definitely follow @Odd Ducktreatment protocol Expel p is safe to use with invertebrates I have used praziquantel and levamisole in the past and never had it kill my beneficial bacteria

With the symptoms your describing and the weight loss that point's to a parasitic infection @Odd Duckhas a good treatment protocol for parasitic infections that I would follow

I just read an article about scarlet basis recommended temperature is 72-79 your tank will probably get to cold for them at certain times of the year unless you add a heater

With the colour loss could be caused by stress if he's getting bullied or you can get this colour loss with a bacterial or parasitic infection with some of the symptoms your describing what I would do is treat with paracleanse every two weeks for a total of three full course of treatment I would also add some aquarium salt 1 table spoon for 10 gallons at that level it won't harm your plants the salt will aid Gill function and add essential electrolytes I would also follow up with a course of maracyn after the first course of paracleanse if your not seeing any improvement add an extra air stone during treatment @MattyM

That doesn't look like columnaris or ich possible fungal infections or epistylis what I would do is treat with ick X and aquarium salt 1 table spoon for 2 gallons for one week I would recommend getting some test strips so you can keep a close eye on your water parameters during treatment I would also retest the water parameters in your main tank just in case something off usually when fish start to hide or go off their food its a sign of poor water quality stress or disease @HorohoTank

It could be the hillstream loach are stressing the khuli loach in a 55 gallon their should be plenty of room for the two species

With columnaris a temperature below 75 slows spread but I wouldn't go below 75 with kuhli loach depending of the species of hillstream loach you can keep them at 65-80 the bacteria that cause columnaris is always in the your tank it's time of stress or poor water quality that weaken there immune system is when you get outbreaks it doesn't necessarily mean your Cory's are inflected that you give the breeder or the hillstream loach were the carrier's I would have separate nets and buckets for each tank if you can and steriliser them with a 3% hydrogen peroxide solution

With columnaris you get white patches on the back white lips that can turn into mouth rot it spread more quickly at higher temperatures and can kill your fish anywhere from 24hr to 7days depending on the strain if you can get a picture that would be great what I would do is a course of jungal fungus clear fizz tabs containing nitrofurazone now and add some aquarium salt 1 table spoon for 5 gallons at that level it shouldn't harm your plants and it will aid Gill function and add essential electrolytes till the kanaplex arrives it's always possible that your kuhli loach injured it's self and it doesn't have columnaris I would always air on the side of caution if your fish have white patches follow up with this treatment plan @KittenFishMom

I wouldn't recommend kanaplex in food as it's poorly absorbed by the intestinal tract it's not very effective in food you could dose the tank with kanaplex and add the metroplex to food

From what I have read they do best at 75-82

Looks weak any rapid breathing listlessness flashing spitting food out loss of appetite it might be the way his body is bent it looks like it has a bit of a sunken belly correct me if am wrong on that @memorywrangler

It could have a broken jaw or mouth rot that's eaten away at the jaw in that case it might be best to humanely euthanize it with clove oil @cinnanoodles

antibiotic treatments such as Maracyn2 or kanaplex are fine to use with whiptails

You usually get mass mortality with columnaris not the odd random deaths I still couldn't rule out a bacterial infections with this angelfish so still think it would be beneficial to do a course of maracyn2 or kanaplex just in case there's a bacterial component

What your pH and KH as kuhli loach like soft acidic water pH 5.5-6.5 I wouldn't recommend medicating new fish that are already stressed and possibly weak I would just monitor for any signs of disease in quarantine for a minimum of 4 weeks as medication could push already weak fish over the edge I would add some Indian almond leaves as they have antibacterial and antifungal properties and will provide some cover for them @JackalTattoo

There's a couple of treatment options if it were a confirmed case of the columnaris as it's a gram negative bacterial infections that spreads more quickly at higher temperatures and can kill fish anywhere from 24hr to 7 days depending on the stain the Most effective treatment I have found is a combination of kanaplex and jungal fungus clear fizz tabs containing nitrofurazone following this treatment plan if your not sure it's columnaris then I would just do a course of maracyn2 or kanaplex I wouldn't add methylene blue to your tank it will kill your benefial bacterial high levels of salt can be effective at the level need it would be harmful to your catfish

I think it combination of things they got chilled that coupled with the high levels of ammonia and nitrite has affected there immune system leaving them susceptible to secondary infections I would keep doing daily water changes and just add prime and stability adding all these other water treatment can stress your fish out and dramatically lower the levels of desloved oxygen if you can get holed of some cycled media from your lfs or another tank that will help speed up the cycling process I would also add some aquarium salt 1 table spoon for 2 gallons salt speeds up the removal of ammonia from your fish blood and also provent the uptake of nitrite and it will aid Gill function and add essential electrolytes and I would add some Indian almond leaves as they have antibacterial and antifungal properties add another air stone to increase levels of desloved oxygen i would monitor for the next couple of days @TJfm1990

White mouth can also be a sign of mouth rot often associated with columnaris I would air on the side of caution and do a course of maracyn2 or kanaplex just in case there's a bacterial component

dose medication wait 24hr then you can do as many water changes as like before redosing the medication the following week

Have you tried crushing the shells of your snails then dropping them in it might be easy for him to swallow

Theirs always a possibility that antibiotic treatment will kill off some of your benefial bacterial there's a lot of debate on bottled bacteria I think it doesn't do anything to help speed up the cycling process just my opinion if I have a wobble in my cycle I do 50% water changes daily and add a double dose of prime every 24hr to help detoxify any ammonia and nitrite till it constantly stays at zero if you have other tanks you can always take some cycled media from that @Guppy Guy