Can I transfer my present SBI Savings account in zero balance account?

I have savings account in State Bank of India. I have taken cheque book facility, ATM card and net banking facility. Can I transfer this account into zero balance account? My transaction goes to a very up down level as near to 50 Rs or 50000 . But I cant maintain a minimum balance in it. Please help if you know details about it. Otherwise no need to waste the time. Thanks in Advance.

Do I need to pay estimated taxes quarterly if I make enough trading stocks?

I have a full time job and have started trading stocks few months back. Already I have enough realized gains that will force me to pay additional tax. My question is do I need to pay estimated taxes quarterly based on the profits I have made so far or can I wait till the end of the year to pay my taxes.
Any one who has been in this situation, if you can share your experience, it will be greatly appreciated.