what could it be?

i have a general hydroponic rainforest system. there are six inserts all running smoothly except one of them.the hydroton in one of the baskets for some reason will not stay moist it is always dry to the bone. i think it may be a issue with the level of the Reservoir? but im not sure everytime i take it out to look water pours off of it but it still stays dry!
 
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