Not accepted as of Dec 7 2017.

From Maggie-sensei:

重い　( = omoi) & 重たい ( = omotai) both have the same meaning: “heavy” . We don’t usually distinguish between them very much but I think 重たい ( = omotai）is a bit stronger than 重い ( = omoi).

重い ( = omoi) is objective and 重たい ( = omotai) is subjective. So if you carry it yourself and feel the weight, you use 重たい ( = omotai)

Japanese -i adjectives have to change form to reflect negation and tense, so you must change 重い (omoi) to 重くない (omokunai).