Colu

I can see a little bit of red near the mouth if your going to dose Jungal fungus clear fizz tabs and kanaplex use this treatment plan it's for more severe bacterial infections

Easy green is nitrogen based fertilizer so that will increase your nitrates that what's happening her

30-40 ppm of nitrates won't harm your Cory's once your floating plants start to spread they will start to remove a lot of the nitrates from your tank you could add some quick growing stem plants like hornwort or Elodea are you adding any fertilizer that would be adding nitrates to your tank like the co-op easy green

In Canada kanaplex and other antibiotic treatment aren't available unless you see a vet Keep up with salt and Indian almond leaves update in week or sooner if he get worse

Looks like it has a sunken belly you could try feeding him up and monitor for a couple of days to see if he starts to put on weight if he doesn't then I would treat with Expel p once a week for 4 weeks I would treat all the guppies @Sherry

If he's more bloated and your not seeing any improvement with the medicated food i would stop treating with the medicated food I think we can rule out over eating and constipation as fasting and Epsom salt baths haven't worked internal bacterial less likely given the length of time possible parasitic infections other than the bloating he isn't displaying any other symptoms possible internal growth which there's no treatment available you could treat for a parastic infection or just monitor him if he's active and eating ok or you could do a course of anti-parasitic medication such as Expel p or paracleanse I don't think they would be beneficial at this point @nic

I can't see your pH fluctuating 0.5 -0.8 causing the problems your seeing some fish are more sensitive to swings in pH what your other water parameters ammonia nitrite nitrate

The white patch looks like an injury what I would do is keep the salt at 1 table spoon for 1 gallon for a week and add some Indian almond leaves as they have antibacterial and antifungal properties depending on the quality of leaves you might have to add one leaf per gallon and I would also do a course of kanaplex am going to tag @Guppysnail has more experience with snails

Have you added anything new such as rocks that would be raising your pH

What was your pH before it spiked

It probably started with barbel erosion with anything bacterial it's difficult to say for sure weather it will spread to your other Cory's with out noing the stain of bacteria involved I tend to be overly cautious when it come to disease you could treat them together there's always a possibility that something might spread to your other fish

Looks bacterial possibly the start of mouth rot kanaplex and salt should do the trick

With symptoms your describing I would treat for bacterial infection it could possibly be aeromonas that's a gram negative bacteria what I would do is treat with a combination of maracyn2 in food feeding a small amount twice a day for 7 days active ingredient minocycline also has anti-inflammatory properties and dose the tank with metroplex @IHOctopus

I would go with the shrimp sounds like your tank going to perfect for them

As plecos are more sensitive to salt what would do is start at 1 table spoon for 4 gallons for two days then increase it to 1 table spoon for 3 gallons for another 3 days do the Epsom salt baths for no more than 15 minutes

Swiss tropicals has them in stock in the USA

Ats has some great books if your into catfish they are bringing one out on bristlenose that been delayed in the next couple of months first two books they are great read @TeeJay

Looks like epistylis the most effective treatment is maracyn2 in food and dose the tank with ick X as epistylis feeds off of gram negative bacteria on the slime coat on your fish and spreads more quickly at higher temperatures you can use this medicated food recipe with rapshy if he's not eating dose the tank with maracyn2 I would add an extra air stone during treatment @syzygy

As your ammonia at zero if the temperature 80-82 what I would do is a couse of seachems kanaplex it's a very effective antibiotic treatment for gram negative bacteria as most cases of fin rot are caused by gram negative

Assuming this isn't a typo If your ammonia at 15ppm you need to immediately start doing daily X2 water changes of 40% you can add 5x time amount of seachems prime in an emergency to help detoxify any ammonia till it constantly stays at zero that level of ammonia can kill your fish and what causing the lack of appetite and fin rot not amount of medication will work with ammonia at that level temperature bettas do best at 80-82

Little more information would be helpful what are your water parameters ammonia nitrite nitrate pH temperature what type of filter are you using it's difficult to tell off your picture any redding to the edges of the fins @dragon enjoyer

As you have treated with salt and maracyn and not seen much improvement it more than likely an injury to the eye and it might need some time before you see any improvement what I would do is leave it two weeks without any treatment and just monitor update if he's gets worse before then

If the spots are raised I would treat for epistylis if the spots are flat I would treat for ich the treatment for epistylis a combination of maracyn2 in food and ick X will also treat ich going off your picture I would be leaning towards epistylis

The spots look raised if that's the case your more than likely dealing with epistylis it feeds off of gram negative bacteria on the slime coat of your fish leading to secondary infections that's what usually kills your fish and it spreads more quickly at higher temperatures he's how you tell the difference between ich and epistylis if epistylis you want to do a course of maracyn2 in food feeding a small amount twice a day for 7 days and dose the tank with ick X or aquarium salt as you have a lot of live plants I would use ick X @mikewxyz

Add 1 table spoon for 2 gallons add on day one only put back in what you take out so if you do a two gallon water change put 1 table spoon of salt back in