Originally Posted by SassyBetta
ok to bettaluvies
his set up consists of a split 10 gallon tank ( but the reason i think hes stressed is cuz of the fact that he was my first and because of that he had all 10 gallons to himself at one point befor i split it , i think hes stressed about the loss of space < and i feel bad i didnt think about it till way later :( ) he has 3 soft silk plants of varing hights and a nice betta cave made from a coffy cup. this is also true with the other side of the tank that houses my vt betta pomidor. they can see each other but they dont really ever flare at each other, just 2 days ago pomidor flared at obsidian and then i noticed his shreaded tail,
I would say it's definitely the presence of the other male, rather than the loss of space that is causing Obsidian to tail bite.
Even if you don't see them flare at each other often, it could be that Obsidian is naturally submissive and so there's not that constant battle for dominance between them.
However, if that's the case, Obsidian could be feeling vulnerable and this is what is causing him to bite his tail.
You could try moving the silk plants so that they run down the divider on both sides to provide a visual obstruction if you haven't already done so. One out of 30 of my bettas regularly uses his PVC pipe cave, and I've found plant cover to be much more important in reducing stress.
Floating plants are especially favoured by my less aggressive bettas to hide in. That way Obsidian might feel like he has somewhere to go that he feels safe.