I got some Heterandria formosa and the fish were really small how big do they get?

Biggest female I ever saw was almost an inch. Never saw a male that reached half that. They are the smallest vertebrate in North America, or they were.

Are they easy to breed? And what are the water requirements?

A tank with a small filter does just fine. I haven't tested my water but I have had fromosa for about a week and a half and I already have 3 fry.

How big are the fry?

The fry are about 1/8 inch long

I keep mine in a 10 gallon with no adjustments to my tap water. In my case tap water runs fairly hard with a pH of about 7.8. In the tank it is sometimes as low as pH 7.6. My biggest male is close to 3/4 inch long and a female sometimes gets to be a full inch. If you take pictures and blow them up they can look quite big, like these guys.

A female



A male



The same female next to a Corydoras pygmaeus. The big one is the cory.

Females get to 3/4 inch, to perhaps on 1 inch on older females. Males can be much smaller to almost 3/4 of an inch. You can keep pairs in quart jars if you run out of room. The fry are t i n y.

OldMan has them in harder water - mine are breeding like roaches in pH 6.6, 40ppm tapwater. The temperature ranges from 18-23 celsius.
They are very adaptable.

I have'nt posted much on here at all, but as far as size, for an example, My wife and I started collecting alittle about 3 years ago in the florida panhandle where my mother-in -law lives (visitings not so bad if you spend it in a muddy canal), this year is the first time we found any Het formosa in the area and all I could net were females, and that was a challenge cause even pregnant ones could wiggle right through the small mesh nets we have so I had to get a brine shrimp net to finally collect acouple of males. With these I'm sure "locale" not that important, but I just wanted to keep a colony from this area...
alittle long a story
Rob & Amy