Platys and BST

[lina]

I have 5 platys in my 20 gal and was looking for some black skirt tetras to add in. How many should I put?

 

[Slaphppy7]

Platys are hard water fish, tetras prefer soft water...what is the hardness of your source water?

BS tetras can be nippy and aggressive, as well, especially when kept in inadequate numbers

 

[Essjay]

If you are mains water you should be able to find your hardness on your water provider's website. You need a number and the unit of measurement as there are several units they could use.

 

[GaryE]

One of the reasons black skirts/widows etc are popular is they are extremely adaptable to harder water. Being with platys doesn't bother them - they'll even breed in moderately hard water.. This isn't the old fable about acclimating through generations of captive breeding. This is a fish that never seems to have specialized for any narrow water needs, unlike many other tetras.

The bigger problem if you pop a group into a 20 is how large they grow. Don't base their size on the youngsters sold in stores. They grow.

I wouldn't put G. ternetzi in the group, but there are a number of hardwater tetra species. I've been nibbled on by tetras in rivers with swordtails and mollies in them. Every species is different.

 

[Byron]

Agree with others. A 20g tank is not sufficient space for a group of Black Skirt/Widow Tetras. They grow, they need a group of around 12, and they have a not very nice disposition which means in smaller groups they are even more aggressive.

Five platys in a 20g if this is a standard (sometimes called high) 20g is a lot more fish than you may realize now. They grow too.

 

[emeraldking]

Don't base their size on the youngsters sold in stores.

This is one of the problems many people are dealing with. At stores a lot of fish are sold at a size that is of a juvenile. And many people take that as a reference and not knowing how big they can actually get.