Need Stocking Suggestions for a 20 Gallon

Moldau

Hello, everyone! I have a 20 gallon aquarium that I have been trying to decide how to stock. Here are some things I have to consider:

1. I already have gravel for the tank, so I don't want to get fish that require sand.
2. The water here is very hard and alkaline (pH around 8.0-8.2, I have had a bad time keeping many of the tetra species, and I want to get fish that will do fine in this water)
3. The tank is not the "long" kind, it is 24 inches across the front

Some preferences:
1. I want to have a good variety and distribution of fish throughout the aquarium (top, middle, and bottom dwellers)
2. I like bettas, so a combination involving a betta (male or female) would be good, however that does limit my choices so I want to consider other combinations as well. One stocking I've heard of is a betta, a school of harlequin rasboras, and some kind of bottom-dweller. However, I've read conflicting information about keeping harlequins in hard alkaline water. I also know keeping bettas with tankmates is risky, so I want to consider non-betta combinations as well.
3. If I have any kind of livebearers, I want a single-sex school because I don't want to deal with a bunch of fry all the time, regardless of whether they all get eaten.
4. I want this to be a peaceful tank with hardy fish species.

Thanks in advance to anyone who reads all this and gives suggestions!

PRichs87

Swordtails are the fish fish that jump out to your requirements, but I wouldn't keep those with a betta, too similar.

gingerael

swordtails, mollies, Platy's or guppies would make good middle to top fish. bottom of the tank can be taken care of by cory catfish, which are a good smaller type fish.

Steph211

I love african dwarf frogs. They get along just fine with my betta. I have gravel substrate too and a 20 g. I also have a school of cardinal tetras. Everyone coexists very peacefully.

The frogs are very active later in the day and are pretty hardy and cope with a fair range of water parameters. I feed them sinking frog pellets or bloodworms. The only thing you have to be careful with is that your other fish don't get the frogs' food before they do. My betta and my tetra don't mess with the frog pellets so I tend to stick with those for the ADFs now.

PRichs87

Cardinals would die in hard water.

Steph211

I wasn't suggesting cardinals for Moldau's tank, just the ADFs. Also it can be tricky when dealing with a betta. I had frogs first and then added the betta. For the first few hours, as he got used to the tank, the betta did take a few nips at the frogs' legs. Honestly, I think he'd never seen them before and perhaps thought they were worms. Once he realized his mistake, he's never bothered them again. In fact, sometimes my frogs will accidentally bump into the betta on their way to the surface and the betta doesn't seem to mind at all.

gingerael

I've found that ADF's can be major fin nippers since they are next blind and can really only see light and maybe some blurry objects. I wouldn't recommend them with any long finned fish.

Moldau

Thanks for the suggestions, everyone!

@gingerael, I like cories, they seem like fun fish to have, but I have often heard that you should have a sand bottom tank to keep them. Also, I thought they were more soft water/neutral pH fish.

@PRichs87, Out of curiosity, is there any reason why you suggest swordtails in particular? I've never actually known the difference between swordtails and platies, other than the tails.

PRichs87

They are a very easy fish to care for and aren't demanding, minus the hard water. They come in a variety of colors. If you do opt for them, be sure to have 1 male for every 2 females.

Moldau

Since I want to avoid them breeding, would swordtails or other livebearers be okay in a group of just males or just females?