Adding to the Tank

[Tinanewfishmom]

I would love some advice! We have a 20gal tank right now. We had 3 mollies, but I found out we had 2 male and 1 female- really bad. The LFS agreed to let us return one male, so we returned the alpha male. Our other male was bullied by the alpha and is now in quarantine (5.5gal) recovering from illness and our female is still in the 20g and also seems to be recovering from the stress of both boys well. After a week or so when our male is recovered I was hoping to add another female molly, but I have learned that 1. it's better to quarantine the new fish for a few weeks and 2. even a 2-1 f/m ratio is low. So I was thinking it would be better to add 2 new females to the quarantine tank and then add all 3? mollies to the 20g tank after a couple weeks. However, I am worried that our 5.5gal is too small for 1 molly...and certainly three. I am also worried that adding three fish might be too many at once for our tank. We originally wanted 3 platys, 3 mollys, a bristlenose and another fish, which we decided on a betta. I am further worried that a 4th molly would overstock us. I would love to know how you would handle this!

 

[Byron]

Betta (assuming a male) is not a community fish. Male betta should be on its own, in a 5g tank or larger, but alone.

There is another issue here and that is the water parameters. Betta prefer soft water, whereas mollies and platies (livebearers) must have moderately hard or harder water. Mollies are especially sensitive to soft or acidic water and they will not last very long. I only mention this because the water for livebearers and a betta is not the same, or shouldn't be.

The other thing is the tank size...20g (presumably a standard or high 20) is very small fort mollies; males reach 3 inches, females up to five inches and some report six inches. You are correct that one male should have three females preferably to spread his attention around, but you will have dozens of fry every month and they are not that easy to get rid of, nor will they all get eaten. The platies will be the same issue if male/female are present.

In a standard 20g the platies will work, but not mollies or both. With livebearers, males only is usually better unless you specifically want to raise fry, but as I said you will then have to dispose of them somewhere.

Quarantine tank size is less of an issue than the permanent tank home. This is because most fish from stores will be juvenile and not fully grown, plus they are only in the QT for a few weeks at most, and additional water changes can be done if needed depending how many fish. The permanent tank in which the fish will live the rest of their lives is a very different thing, and it must be suited to the mature sized fish if the fish are to be healthy and develop properly.