Welcome aboard Surya_kant31...
You'll love it here...Looks like you have a pretty good sized tank..I LOVE big tanks..Wish I could get more of them. I see in your aquarium Info you don't know about the Nitro cycle.
Heres a link that explains it.
http://www.fishlore.com/NitrogenCycle.htm
You must be doing something right if your aquarium is 2 years old but this will give you a better idea of what's going on behind the scenes. Nice to have your hear..We love pics so share any you can. Again..Welcome to Fishlore.
Edit
Just saw another thread with all your pics..Adorable...Good looking fish
