Oral lesions (mouth sores) make it painful to eat and talk. Two of the most common recurrent oral lesions are fever blisters (also known as cold sores) and canker sores. Though similar, fever blisters and canker sores have important differences.
You could do a school of White Cloud minnows, they require cooler water, so you wouldn't need a heater. I think if you check the profiles, the ideal temp should be no lower than 67 degrees. Not positive.or example: my goldfish tank is fine in the summer, but my house gets so cold in the winter that I need to have a heater to keep it above 70F. Fish need a constant temperature which is one of the reasons we use heaters.
Use a granular filter cleaner for you hot tub, like Power Soak or Eco Soak, to clean your filter every 3-4 months. Also use the cleanser on your filter every time you replace the water in your tub. Replace the dirty filter with a new, clean filter while your dirty filter is being cleaned.