Interesting! I've always done something similar with my bettas each time I've gotten them (putting them from the bags/containers into my 1gal sick bowl, after an hr adding a couple tbs of tank water, then another every 15min until the bowl is almost full. Then I net & transfer.)
I'm hopeful #4 makes it he was swimming around normal for a bit but then went right back to sideways against the corner. now is back under the 1 plant. I hope in the morning he'll be back to normal, the new female is doing just fine together with the other female & my original male. It's amazing just how easy it is to tell the difference is shape & body color on these guys if you really look at them!
30gal Planted; Mollys; Dalmations: Sailfin(M), Balloon (F) & Common (F). Sunset Common(F), Julii Corys, Otto Suckermouth Catfish, Hillstream Loach, Leopard Loach, Clown Pleco, Blue Mystery Snail, Tetra's; BlackSkirt, Diamond, Black Phantom, Serapae.10gal Planted; Eeyore (Super Delta Marbled Betta M), hasbrosus Cory, Scissortail & Harlequin Rasbora's, black Neon & neon Tetra's, Otto Suckermouth Catfish. 2gal:group male guppies