Ok, so at this point Odysseus has been battling fin rot/tail biting/torn fins for over a month. I'll answer these in one post, then add a narrative in a reply so that this stays readable.
What size is your tank? 3 Gallon
What temperature is your tank? 80-81 Degrees F
Does your tank have a filter? Yes, Undergravel
Does your tank have an air stone or other type of aeration? Yes, air-stone driven UGF.
Is your tank heated? Yes, Hydor Theo 25 watt.
What tank mates does your betta fish live with? Marimo balls
What type of food do you feed your betta fish? NLS Betta or Omega One Betta Buffet Pellets, alternating weeks, although he seems to do better with OO.
How often do you feed your betta fish? 2x per day, usually 3 Omega One pellets each morning and night.
How often do you perform a water change? At least 2x/week.
What percentage of the water do you change when you perform a water change? 90-100%
What type of additives do you add to the water when you perform a water change? Prime and Stress Coat.
Have you tested your water? If so, what are the following parameters? Just changed water yesterday evening, but in general:
Hardness:N/A, but the water here is VERY hard.
Alkalinity: N/A, but likely high (see Ph)
Symptoms and Treatment
How has your betta fish's appearance changed? Fins keep tattering, shredding, occasionally he'll have taken maybe 2 bites from the tail. Redness near the shredded area. Dorsal fin never really got better.
How has your betta fish's behavior changed? Hangs around the bottom of the tank more, and is a little lethargic.
When did you start noticing the symptoms? Evening of Jan 1, 2013
Have you started treating your fish? If so, how? Aq Salt, Stress Coat, Kanaplex, frequent water changes.
Does your fish have any history of being ill? Not before this started.
How old is your fish (approximately)? Got him in November 2012, he seemed full grown then, so probably a bit over a year.