Urgent mystery: what could be stressing my betta???

Greetings, and thanks to aquariacentral for being such a great resource for fish keepers everywhere!

I am keeping bettas again, and am having a problem with one of them! I recently acquired a beautiful red copper and black halfmoon, and transferred him to a 2 gallon heated, filtered, cycled tank. Since putting him in there (5 days ago) he's shown worsening signs of stress, and I am totally unable to explain it- I've considered every possible cause! I see no sign of infection or disease, but his face is badly striped 80% of the time and his tail is beginning to fray. He is still curious and lively, in fact sometimes he swims spastically as though something in the water is bothering him, but as you'll see below, I've ruled out all the usual suspects. I feel sure he will continue to deteriorate fast unless I address the cause of his discomfort/agitation.

2 gallons
0.5 teaspoon aquarium salt added concurrent with fish (5 days ago)
tank is a constant 79 degrees
filtration is a small DIY sponge filter - no current to speak of, and only a faint humming noise
AM=0/NI=0/NA=negligible/pH 7.6+
Tankmates: none
Substrate: none - bare bottom hex tank with a piece of white pvc for a hiding place.

Troubleshooting so far:

• His bright LED lights are not the problem, as two days of ambient light only has not improved him
• I ran a small hob filter with brand new chemi-pure for an hour to rule out the possibility of contaminants - no improvement.
• I blocked the line of sight between his tank and the tank of my second betta (who is thriving) in case they were spotting eachother too often. This has made some improvement in his manic swimming, but his stripes are still bad.
• Started him on Kanaplex last night to rule out some kind of pathogen. In other cases of bacterial/fungal affliction this has produced immediate results, but I see no improvement in him thus far.

Any ideas or advice would be greatly appreciated, as I do feel sure I will loose him if I can't solve the mystery.

Thanks so much for your help and support!

Prerttyfish

I put him in the day after it tested perfect (I did a fishless cycle with safe-start), and continued to monitor the water parameters closely for the next couple of days. No problems.

Thank you so much for the responses and ideas.

I am actually in the process of setting up a different tank for him (don't want to give him my little dragon plakat's tank because that fish is blooming and healthy and I don't want to mess with any part of his world).

Stray electrical current is something I've never considered. The only thing it could be is the heater, as his filter runs off an external air pump. I'll definitely investigate.

The reason there's no substrate at the moment is that the tank design is a work in progress. I'm planning an unusual setup, and I wanted to make sure the fish was healthy and well-adjusted before I start adding things that could complicate the picture. From what I hear, many people (especially breeders) keep bettas in plain tanks with no ill-effect, but maybe I'll add some temporary plants to see if it helps. Very good point about the possible reflectivity of the bottom, too, although he seems to spend most of his time up and down the sides. I'll look into it.

He seems to have stabilized a bit since I blocked my other fish from view and dosed him with KanaPlex, his tail is the same as yesterday and his face, though still not coal-black, is not so striped. I don't think the problem is solved, but I'm glad he's not continuing to get worse.

Will keep working on it and post back if anything changes! :huh: