Smaller Tank

[kiriyama]

Hi , I am very new to fishkeeping , I have had a disaster and lost a few of my Lemon Tetras last night. For future referance I want to get a small second tank , hospital , quarantine , breeding? What would be a suitable size , I am in a very small house and the room the tank would be in maybe 12" or 18". Is this ok or still to small ? What size heater would I need?
Thank you in advance for any replies.....

 

[aly_starh]

18" would be better IMO, a 50w or 100w would be good!