Hi...

i have one oscar, he is about 15cm long and is at about 11 months old, n is ALWAYS hungry!!

i feel him tiwce daily on pellets that i have brought him up on (not sure how many), every fortnight i feed him about 20 live fish, and on top of that my sister feeds him at ramdom occasions cause she feels "sorry for him"

as he is still quite young, am i not feeding him enought??

basically, you could feed your o what it can consumed
in 2 minutes. whatever left should be removed to lessen
bio-loads.

how big is your tanks? 15 cm is approximately 6"long,
relatively small for an 11 month old oscar.

Yeah i kinda stunted his groth when he was younger...

but he is now in at 4ft tank..

with a bigger tank, i will grow fast. just keep your water
in healthy condition. fish gain 35% of the food it can consume.
if you give it 1.0 kg in one month, it will gain additional 350
grams in weight in that span of time until they reach maturity.
upon reaching 12 inches long, it will slow down the growth.

jsut roughly will a 4ft tank be big enought for one adult oscar?? or do u think i will need to up grade again int he future???

in the normal rearing of oscar, yes. but since you had keep the oscar in the 30 gal tank for quite sometime, it can survive again for another year. but the question is, will it be happy? will you enjoy changing water a lot? dont you want a company for it?

is your tank 4ft x 18" x 18" or 48" x 18" x 21"?

as long as your tank is a minimun of 55 gallons your oscar should be fine in it for life but it will not be big enough for tankmates. if you can give us all the tank dimensions we will be better able to properly answer your question.