Mini-cycled

[i have crabs]

only reason i could guess is if you stirred up your sandbed while adding the new water, other than that i dont see anyreason you could get anytype of cycle from changing water,
like i said in your other thread, dont use phosguard with any leathers in your tank, they usually live but sometimes they dont recover,

if you have any prime, add a cap of that it will detoxify the amonia/nitrite just for a bit extra saftey, if you dont have prime i wouldnt worry about it.

do you use ro/di water? what do you feed the tank?