I know that it is not a good idea to use fertilizer that has been diluted for a long time. Try keeping your fertilize in a plastic storage bin that is air tight. Maybe it will last longer for you that way. As to if this fertilizer is still good, I am going to go out on a limb and guess that it has degraded in potency. It probably is not 'bad', but probably is not as strong as it was when new. JMHO I would try using it and if I did not get the results I expected, then I would get new.