That is my worry, "Generally". If it happens melt down (perhaps
pH dependent, check the instruction), could cause major problem. I've seen it melt down before its time.
Also had occassion where fish did not even touched the blocks.
For long trips, I depend on Auto Feeder (always hook up weeks before the trip to make sure all are working properly). Even Auto Feeders will fail due to moisture from tank can cake up the flakes to a point mold/fungus grow. Will talk about how to modify Auto Feeder next time.
For 8 days, fasting would be better/safer choice.