Originally Posted by Fishta
i would probably get a 10 gallon tank. the PH value is about 7-9, Hardness (as in CaCO3) 50 -120. the tap water in my country is potable so does that help? Total Alkalinity (as CaCO3) 20 - 60 10 -50 @ Total Hardness (as CaCO3) 50 - 120
"Potable" means safe for drinking. But what is safe for humans is not necessarily safe for fish.
The hardness is OK, I am assuming those numbers are parts per million (ppm). The pH fluctuation from 7 to 9 is dangerous. If it is that variable, you will need to check the pH prior to each water change to avoid too great a fluctuation. Once a tank is established with fish, the pH will naturally settle and it should not fluctuate much or the fish will be stressed.
As for fish, in a 10g you do not have a lot of room. Neon tetra were mentioned, so a group of 7 would be OK (with live plants) and perhaps a bottom fish, like a trio of Corydoras, or a small species of catfish.
Other options are smaller fish, such as Ember Tetra, one of the dwarf rasbora like Boraras brigittae, or Dario dario. With these "dwarf" species, a group of 7 of 2 species would be nice, providing a bit more interest with different colour and behaviours. And one of the dwarf cory species, a group of 7? There are lots of options with small fish.
We have fish profiles here, second tab from the left in the blue bar across the top of the page, and you will find many fish species under the characins and cyprinids sections with information on tank size, water, compatibility, etc. When a fish name is shaded in a post, it means that species is included in the profiles and you can click on the shaded name to see the profile, example Pygmy Cory.