There's something wrong there if that's happening that quickly. I've used mine to season several humis, with no problems and not running out of water once.
First thing... perhaps you have never put enough water in the CO! Hopefully you have a syringe (available from any drugstore), as it makes getting the distilled water in the little hole a billion times easier, and you can monitor how much you put in. Keep putting it in there until you can see it that it SLOWLY is soaking into the sponge (or whatever it is) inside, and perhaps can see a little bit of shine such that you know water is almost saturating the sponge. And do this in both holes!
Finally, I wouldn't set it at 78%. I'd set it at 70%... as you want the humi to be seasoned at whatever your interior humidity will be. If you oversaturate the humi, it won't hurt anything, really... but it will make stabilization a bit screwier as the humi releases humidity, raising your interior rh, until it equalizes. And maybe requesting that RH get to 78% really requires a ton of water? (Don't know if an 8% rise in RH requires substantially more than an additional 8% h2o?)
Anyway... good luck! But it should be easier than it has been. So, either you've not added enough water, or you have a more significant problem, most likely a very leaky humi. I'd give it a go at refilling the CO with copious amounts of water, and trying again for 70%, or maybe 1-2 rh higher.