20 Gal Tank With Female Bettas?

[khial]

I have a male in a 5 g tank in my office area. He's suffering from finrot but I can't figure out why (It's not my water quality, I checked) I'm going out to buy some medication for him today,
He's a really lovely boy, (Or was when he had his fins) 
I don't know what sort of Betta he is, I asked when I first got him and he was labeled as 'Fancy'.... which didn't help

it just made him more expensive, can anyone tell me what he is? i.e: VT, HM ect..ect..

He's looking rather ragged now

There's no other fish in the tank so I'm guessing he either had something from the store or I haven't been caring for him as well as I could be and he's gotten sick

 
 
Anyways, if I were to add 6-8 females to the 20 G, all at the same time, wouldn't that stress the filter with the sudden extra load?
 
Also, as there is this auction where I plan to be buying some/all of them, is there anything else I should buy? I've been to this previously and there are a lot of plants being sold, any particular types I should look for? I have Java Fern and Amazon Swords and Annubias(sp?) on my list, but I already have those anyways, Are there other types of plants out there that they like? Their fins aren't as large as males so I assume I may have the option of buying fewer broad leaf plants and go for more of a variety?

 
 
I think he may possibly be a Delta,
 
Pictures not the best to tell.......You know best on what he looks like with his fins in good health and flared up so i would look it up on google images....there are definitely some similarities from what i can tell on the picture

What substrate are you using by the way?

 

[KrystaK]

I've had him for over a month and I've never seen him flare! Even in the store he didn't flare
As far as when he had fins, I have a few other pictures, and there was a discussion on what he could be, but I don't think everyone ever agreed. It came down to either Delta (or Super Delta) or HM, or some half breed variant of the two.. or something....  
 

(Some alternate pictures that have fins from slightly different angles) 
 
I now have a fine white sand substrate, but at the time of this picture if was  black sand mixed with a dark rather gravely plant supporting substrate. So it was a mix of sand and a few chunks of slightly larger stuff (Like the red bit you can see almost int he middle of the picture...)
 
I'm considering adding smooth gravel to some areas of the tank as the white sand I have is so fine it doesn't really have a texture to it.... and it gets dirty so easily, the vacuum sucks it up more readily than it sucks up the waste. 

 

[khial]

Only reason I ask is because I really want a dark substrate but refuse to pay the amount for black sand, so  I was thinking of going with just a planting substrate and nothing else to replace my gravel...I have regular play sand in 3 other tanks.
 
back on subject...I think he looks more like a Delta than HM, I'm no expert but have looked at ALOT of betta pictures and forums/groups.