He isn't acting weird or anything, behavior is still frisky, no panting, no tail biting, eating well, pooping well, no bloat, no other visible concerns. But along his caudal fin, I noticed some reddish clumping along the edges. I first noticed a spot of it a week ago. THat spot is gone, but now some more have appeared in other places. I check my parameters every other day and ammo and nitrite are always 0, and nitrates are never over 10, usually just 5. Tank mates aren't bothering him, he has tons of hiding spots, I just don't know why he would be getting fin rot?
What size is your tank?---20 Gallon High
What temperature is your tank?---79* (on a rare occasion, it dips to 78, like maybe one day every couple of a weeks, if it's a cold night)
Does your tank have a filter?---Yes, unbaffled Marineland Penguin 150
Does your tank have an air stone or other type of aeration?---Yes, a bubble wand, set to the lowest setting
Is your tank heated?---Yes
What tank mates does your betta fish live with?---in siggy. He occasionally will flare at the platy as she tends to hover near "his" corner, but usually he doesn't care about nor even really appear to notice the presence of the other fish.
What type of food do you feed your betta fish?---I have changed my feeding routine several times til I finally feel ok with it. At first, I fed him Hikari pellets, 5 pellets twice a day. That was for about 2 weeks. He got bloated on those, and I switched to NLS pellets. I give him 3 twice a day, plus he usually sneaks some of the others' Aqueon tropical flakes. If I see him eat a bunch of their flakes, I don't give him his second feeding. I have recently added frozen bloodworms (half a cube) every Friday. I fast everyone on Saturday. He poops fine, and only appears bloated after the bloodworms, as he gorges on those things. His poop appears reddish and blobby.
How often do you feed your betta fish?---see above
How often do you perform a water change?---a 25-30% every week, plus a slight (maybe 1 gallon) stir-dip with turkey baster of the substrate.
What percentage of the water do you change when you perform a water change?---see above
What type of additives do you add to the water when you perform a water change?---API Stress Coat or Seachem Prime (I alternate), per the instructions on the back. Also add some Leaf Zone plant food every week after a water change as well, per the instructions.
Have you tested your water? If so, what are the following parameters?---I use the Master API liquid test kit, testing every day, and I usually skip Wednesday, as I am at school all day)
Nitrate: 5 (occasionally will be 10)
pH: 7.2 (it was 7.6 last weekend before the WC)
Symptoms and Treatment
How has your betta fish's appearance changed?---The tips of his tail have developed a reddish tinged clumpiness along them. The initial spot I noticed a week ago has resolved, but new ones were apparent this morning, all along his caudal fine. There are maybe 4 spots in total, and I would say it's limited to the very edge of his fins.
How has your betta fish's behavior changed?---Not at all. He otherwise is very fit and happy.
When did you start noticing the symptoms?---Last Thursday (Jan 31)
Have you started treating your fish? If so, how?---I tested my parameters immediately, they were all 0 (nitrates were 5), but did my scheduled WC anyway. I added the instructed amount of Seachem Prime and then a small amount of Stress Coat (like, maybe 1/4 the instructed amount)
Does your fish have any history of being ill?---Other than some bloat when he was on the Hikari pellets, which resolved with 2 days of fasting, no.
How old is your fish (approximately)?---We have had him since early December. He looks full grown, or the standard size you see in pet stores. He wasn't a chain store purchase, he was from a small mom-pop store that only keeps a few bettas, and they each have a gallon container, not bags or small cups, and he had no visible illness when we bought him. I QTed him for almost 4 weeks before adding him to the 20G (after the others were added). During that time, we kept him in a 1G container, which I changed the water, 2 50% and 1 100% each week, using tapwater with StressCoat.