spike not growing

[escualida]

Hi all, I currently have four phals that are in spike, they all started at the same time and are growing at different rates, but three of them are already at least one inch long.

There is one, however, that started up and is maybe 1/4 inch long and doesn't seem to be growing much, if at all. Is there something I can be doing to stimulate its growth? Do spikes ever just abort growth?

Thanks!