Backyard Aquaponics
A place to discuss aquaponics

i was wondering if i coulld keep 10 1-2 inch tilapia in a 30 gallon tank for 5 months

Assuming they were 500grams after 5 months, that would give you around 45kg/m3, which is more than twice the recommended stocking density.
So, I think you might struggle, you could always harvest a few as they get bigger I guess.

i need to put them in there until my spring i was hoping to get them fully grown by next december if i bought some 1-2 inch fingerlings

I had some in a 30 gallon tank for awhile, I don't remember how long, but the fish were eventually put outside and had babies of their own in the Summer. Used a 20 gallon gravel bed for filtering with no plants.
viewtopic.php?p=161466#p161466

From what I can tell I had 9 in this from November to May when they went outside. Bred in July/August when the water temp reached mid eighties. All died in the Fall when the water temp went down to 50.

neat little system their i was thinking of a way to keep the tilapia outside over winter next year it involves a greenhouse and a subterranean heating and cooling system