My best guess is that their diet is probably not appropriate for 1 month old hatchlings.
Here's a little copy 'n paste off the Indiana University's site :
"Feed newly hatched, live brine shrimp to young larvae daily. We strain the shrimp out of the brine, resuspend them in axolotl water, and deliver them to the axolotls using a large glass pipette. Feed enough shrimp so that all of the young larvae have orange bellies afterward, but few shrimp are left uneaten in the bowl. Change the water again within 24 hours after feeding, because shrimp cause a rapid deterioration of water quality if many are left uneaten.
When the larvae get to be about 1 1/2" (4 cm) long, we begin to supplement the shrimp diet with pellets. We use soft-moist salmon pellets, a vitamin and mineral fortified, fishmeal-based sinking pellet, 1/8" (3 mm) in diameter (Rangen, Inc.). We gradually wean the larvae off shrimp and increase the number of pellets being offered until the young axolotls are 2-3" (5-8 cm) long, when they no longer need any shrimp.
As the larvae grow, we increase the number of pellets, always seeking to fill the larvae up without leaving a lot of extra food to foul the water.
Young larvae are very vulnerable to disease, but difficult to treat. Therefore, we have found the most effective strategy is to feed them generously, pay particular attention to water quality, guard against overcrowding, and grow them up out of the vulnerable stage as quickly as possible."
Cheers.