WC minnows are active swimmers. 19 liters isn't nearly enough for most fish. That's basically a 5 gallon tank, which is best suited for a single betta and shrimp.
White Cloud Mountain Minnows are highly recommended for smaller tanks, and it's a cold water tank with no heater, so I couldn't have a Betta in it anyway.
I also have lost faith in my 'King British Test Strips' so I'm going to buy an 'API Freshwater Master Test Kit' this evening.
The API kit is a lot more accurate than the test strips- it's an invaluable piece of kit and you'll not regret it
I would say that WCMM do better in larger tanks really. Although they're small fish they are crazy active and like to zip up and down longer tanks. They also need to be kept in groups of 6 or more, which is way more than a 19ltr tank could handle.
Wait... no heater? What about an African Dwarf Frog... Just put some bogwood or tall plants in... so that it can sit with its nose out of the water if it chooses.
Well, I have Platies and Mollies in there at the moment but I'm taking them back to my LFS because it is overstocked and two of my Platies keep getting pregnant.