Flaring Tearing!

[Kytkattin]

Housing
What size is your tank? 5.5 gallons
What temperature is your tank? 82
Does your tank have a filter? Yes, baffled to almost still water.
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes!
What tank mates does your betta fish live with? Another male betta, with a divider between them.

Food
What type of food do you feed your betta fish? Until last week he was fed frozen bloodworms and brine shrimp with some Spectrum a few times a week. Now he only gets Spectrum until I can get some more bloodworms. He also gets Vita-Chem and Seachem Garlic Guard.
How often do you feed your betta fish? Normally once a day, sometimes twice.

Maintenance
How often do you perform a water change? It just now has fish in it after being set up for 2 months, partially drained, and moved 200 miles, so I will be doing 25% daily water changes for this first week.
What percentage of the water do you change when you perform a water change? 25%
What type of additives do you add to the water when you perform a water change? Prime. A lot of it because the water stinks here. Like 5 drops.

Water Parameters:
Have you tested your water? If so, what are the following parameters?
Have not tested yet. I wanted just the ammonia test, but they only sell it with the kit and I couldn't get them to price match it at Petsmart with Amazon.
Ammonia:
Nitrite:
Nitrate:
pH:
Hardness:
Alkalinity:

Symptoms and Treatment
How has your betta fish's appearance changed? His anal fin is split about 1cm.
How has your betta fish's behavior changed? He is flaring a lot, but he still eats and seems normal other than that. He built a bubble nest for the first time since I got him years ago, so he must love the new tank!
When did you start noticing the symptoms? New roommate added last night causing the flaring. Have no way to block their sight of each other, but both sides have lots of hiding spots if they don't want to flare...
Have you started treating your fish? If so, how? No. I don't have any AQ salt with me here, and with the plants I am hesitant to even bother buying any. I don't have a QT tank here, but I could float him in a cup.
Does your fish have any history of being ill? He has had a shredded tail for a long time (years) that is just now started to grow back with a high protein diet. Shortly after I got him he got really sick and nearly died because a plant was shredding his fins, but a heavy salt bath (that also nearly killed him) somehow saved him.
How old is your fish (approximately)? Between 2 and 3 years.

So basically, I am pretty sure that his anal fin will be fine and he should get used to his new "frienemy" pretty soon. With his current rate of fin regrowth on his tail (that has been damaged for years), I would expect it to be healed in a week. I think the new diet is really working! But I figured I would post this just to be on the safe side, or for solutions for two males living together in a divided tank. I can't really add anything like more plants.
Thank you!

[GreenTea]

Well if you have mugs or something you don't use you could create some hiding spots for them, and/or reduce light above their tank. Otherwise it sounds like you kind of have your answer - clean water, food and time. A little aq salt might be in order if you're worried about the split part becoming infected.

[dragonflie]

While I only have a small amount of experience with a divided tank I can tell you how mine have come along.

It's really difficult to completely block their vision, and I've got mine in a 10g where there is more room. As long as they each can retreat I think they will be ok.

It very well will likely take some time for them to become used to their own territories. Watch them very closely for signs too much stress in the meantime. With mine; the "old" betta was the one who was doing the most flaring, and spent the first day doing it most of the day. The next day he was alot more settled into a fairly normal pattern of flaring. Now; each of them come to the divider from time to time and give each other a small display of their prowess; but most of the time all they are concerned about is what is going on outside their tank and when the next meal is coming.

Each is going to have to learn the boundries of their territory, and bettas are not stupid; they will learn that they can't get accross the divider. I think there are probably some bettas who can't handle this transition, so to speak; but as long as you are watching for more serious signs of stress (such as clamped fins, loss of color, stripes, etc.) they should be ok given a little time.

Just make sure you keep the water pristine so no secondary infections have opportunity to take over the torn fin.

[Kytkattin]

GreenTea: They do have their own little caves, anubias plants, a giant rock, and moss balls that all provide some hiding spots. I would love to get some duck weed. Though I could put a whole IAL against the side. That would work when it sinks...

dragonflie: Good to know they should be okay after a while. Thankfully Smaug seems to be in prime condition, otherwise I would be worried about him. The new guy seems much more chill about being next to someone, though being a delta, his tail also seems to be holding up well to all the flaring. It is much more acute than most delta tails that I have seen. I can't even remember what Smaug was... Probably just a delta. At least it is growing back now, hence my hope that this new tear will grow back quickly.

Also, the new guy is very curious about his tank, so he does ignore Smaug most of the time. Lots of fun things to explore!