That's not heavily planted, only 1/4 of the way there
I can still see plenty of gravel! Those swords look new because the leaves look emersed, is that right? Unfortunately, that tank is too small to support so many.. it's probably too small to support even one. With time, they will wither and die off, one by one. Swords are very greedy plants, they'll want lots of iron (for example), so the only way you are likely to keep them alive for long is to have (in my experience) long lighting periods (12+ hours per day or multiple ones) and plenty of root tabs (a 0-0-* fertiliser, I doubt you'll be wanting to add nitrate/ammonium to the water).
13 US gallons / 11 imperial gallons / 50.5 litres volume, and more like 40 litres / 9 imperial gallons / 10.5 US gallons of actual water.
Gravel is not the best substrate for Corys, unfortunately, and 18*12 inches is quite a small bottom area, so personally I would pass on the Corys and go for 8-12 individuals of a dwarf Asian or South American mid-water schooling species. I've created a list of species which go for a 24*12 inch bottom area, which you can find at http
/aquariumadventure.wordpress.com/species-for-a-60-litre-aquariums/ , I think most of the Asian and SA mid-water schooling species form that should be fine with a Betta, when kept in those numbers. If you really want to go for Corys, then I recommend one the Cory species from that list, and 8 individuals as a good starting point (stocking slowly, of course), potentially increasing up to 10-12 sort of numbers.
Actually, having a really long photoperiod (lighting period per day) would make quite a lot of sense as the Otos need lots of algae to eat.. it may be worth trying 14 hour lights per day, to see if that would encourage some.
Because the tank is so deep, I recommend some Java moss for the bogwood, as it can survive with almost no light.
It's really nice to see a Betta in such a large tank, for a change
Edit: your gravel bed does not look that deep.. have you considered pushing all your gravel to the back 1/3 of the tank (adding some sort of divider in front of it) and adding sand to the front 2/3 of the tank? That would be much better for Corys
Edit 2: at one point, when I was still using gravel and had a Betta, I created a two tier substrate and made caves which exited at the bottom layer, but were hidden underneath the higher layer, using clean glass jars. The Betta seemed to like them.
