I cant diagnose whats up

[Ed]

I think the big clue here is that the axoxlotls have been in the tank for 30 days.... I would suspect that the axolotls were suffering from nitrite poisioning which would also fit the description of the symptoms. Depending on the level of exposure, it can take 5 days or more to recover from exposure to nitrite... (for a reference in fish see http://www.vri.cz/docs/vetmed/51-8-423.pdf )

Often the types of sand sold for marine aquaria are crushed coral, dolomite or one of the types of aragonite. All of these can significantly raise the hardness of the tank which is why John was asking about it.

Ed