sorry i missed alot while i was mid typing, im going to go with what wednesday is suggesting and beef up all the seams. if it still is scary on the test fill i can consider the vertival acrylic supports but i do not know if it will be needed. as stated earlier there is alot of tanks that bow as long as the seams are strong i would guess the bowing wouldnt matter much.
im considering cutting the tank in half to get it into the basement, as im bracing all the seams with weldon#40 i could join the tank back together.. just a thought.
another option is to cut the tank to 15' and using the extra 5' as scrap for my joints ect. 2, 10ft tanks would also be an option. ive got a TON to consider