Colu

Could be a type of fungus or mould it probably caused by a combination of low flow and potting soil I would try and increase flow in the affected area you could add ick X and leave it to marinate for week as it treats fungal infections I don't think the mould or fungus will harm your fish @KittenFishMom

I would continue with a small amount of aquarium salt 1 table spoon for 5 gallons almond leaves and clean water for another week and monitor if you notice the redden area getting worse then I would up the level of aquarium salt to 1 table spoon for 2 gallon @Chick-In-Of-TheSea

If your not going away for 24hr I would add some wormer plus do a water change or add carbon before going away remove the medication

Frist I would ask what your lfs water parameters are and do they quarantine you could also dip accumulate them over a longer period of time if you notice them hanging near the surface add an extra air stone

It could be osmotic shock if your lfs stores water was drastically different or low levels of desloved oxygen with them hanging at the surface what I would do is add a double dose of prime with ever water change and I would add a small amount of aquarium salt 1 table spoon for 10 gallons with any new fish @Katherine

Fish Food rapidly lose nutritional value feeding your fish old or spoiled food can lead your fish to suffer from vitamin deficiency and malnutrition leaving them more susceptible to secondary infections

Looks like the start of a tumor their really common in Bettas due to inbreeding their not a lot treatment wise I could recommend if he active and eating and doesn't seem to be suffering then I would leave him to enjoy what ever time he has left bettas can live for a number of years with these types of tumors I would just add some Indian almond leaves and monitor @faded.mallard

Sounds like your Cory has a fungal infections what I would do is treat with ick X and maracyn @Sherry

What I would do is 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 keep your nitrates below 40ppm and monitor if you notice any rapid breathing listlessness hanging near the surface loss of colour then give us an update

If it's swim bladder that can be caused by the fish overeating and the stomach putting pressure on the swim bladder injury or bacterial infection high levels of nitrates and ammonia can also effect the swim bladder if it's the swim bladder what I would do is fast it for a couple of days and do Epsom salt baths 1 table spoon for 2 gallons for no more than 15 minutes as Epsom salt acts as a muscle relaxant to relieve pressure on the swim bladder @Troy328

Cave fish are fascinating more a kin to deep sea fish that evolved in total darkness definitely an interesting species of Catfish

Adding maracyn2 to food is very effective at treating epistylis theirs no need to dose the tank as well if he won't except the medicated food then I would dose the tank and use the aquarium salt as well @Kimber

Possible epistylis doesn't look like ich ich usually has flat spots he's how you tell the difference between ich and epistylis if it's epistylis you want to treat with maracyn2 in food feeding a small amount twice a day for 7 days you can add it to repashy or frozen blood worms and aquarium salt 1 table spoon 5 gallons I wouldn't got above that level of salt as you have live plants epistylis feeds off of gram negative bacterial on the slime coat of your fish and causes secondary infection that what usually kills your fish @Kimber

It does paralyze the worms allowing your fish to pass them repeated treatment will also kill some of the worms I would gravel vac were you can start treating straight away

I have kept bristlenose in soft and hard water over last twenty years and not had any problems bristlenose have been captive breed over a long period of time and are tolerant of a wide range of water parameters I don't think the water hardness changing over the period of a week would kill all the fish @anewbie

Nothing jumping out at me water parameters fine no contamination if it were a disease I wouldn't have expected all the fish to die at the same time without any symptoms from my experience bristlenose are very hardy fish i would have expected them to survived for longer then guppies it were a disease

He's how to tell the difference between ich and epistylis if it's epistylis I would treat kanaplex and aquarium salt 1 table spoon for 5 gallons as epistylis feeds off of the gram negative bacterial on the slime coat of your fish and causes secondary infection that what usually kills your fish kanaplex effectively remove it's food source salt also help to provent secondary bacterial infections @MarkM

I couldn't tell you how good other bands are this is the only one have used in the last couple of years

Your water parameters are ok 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 relieve pressure on the swim bladder @SandBkeeper

I have been using this for two years to temperature match when doing water changes its a lot more accurate than infrared

Difficult to tell off your picture what are your water parameters ammonia nitrite nitrate etc how long has it had the spot any rapid breathing listlessness hanging near the surface @SC Fish

No I wouldn't do another course of kanaplex I would do is a week of salt and almond leaves and then the course of maracyn2 in food if you still seeing no improvement

I can see a tinfoil barbs silver dollars possible giant danio in the left corner that aren't on the list @Birdsnstuff

The only difference in the water parameters was the KH went from 1-8 GH that went from 0-7 I don't think that would have been enough to kill fish as the pH remained stable any possibility of something like air freshener or other cleaning product accidentally getting into the tank usually with mass die off it caused by poor water quality or accidental poisoning with some form of house hold chemical or forgetting to add a water dechlorinator after doing a water change @Chick-In-Of-TheSea

I have that same temperature probe couldn't do without it