oracle - Adding where clientid=x kills execution time of SQL query -

i have query works fast on large dataset:

select q2.*      (select q1.*, rownum rn      (             select name clientname,to_char(callstart+gmt/24,'mm/dd/yyyy hh24:mi:ss') calldate,                  name destination,callno dialednumber,ani accountandcallingnumber,bduration duration,                   to_char(callstart+gmt/24,'yyyy-mm-dd hh24:mi:ss') formattedcalldate,                   switchid, lineno, fileid             cdr                  join client                 on client.id=cdr.aniclientid                 join destination                 on destination.id=cdr.destinationid                 join country                 on destination.countryid=country.id                 join destinationgroup                 on destinationgroup.id=destination.parentid             callstart >= to_date('01/30/2005 06:56:41','mm/dd/yyyy hh24:mi:ss')                 , callstart < to_date('07/16/2015 06:56:41','mm/dd/yyyy hh24:mi:ss')             order callstart desc         ) q1      ) q2 rn >= 0 , rownum <= 10 

this executes in 150 ms. but, when add in line

and aniclientid=363 

above order callstart, query becomes slow, point not usable.

what elegant way fix this?

can done without adding index? adding 1 may politically difficult.

if not, index on aniclientid fix or need 1 on callstart well? believe bitmap index right aniclient column since there 1800 values. index take space?

i'm bit new sql, indexes... in advance!