You only need to change your crystals if they get yucky. Sounds like you are doing everything right - but, yes, you do need to get your ambient temp up. I have heard you can use a UTH on the side of the tub to raise your ambient temp - you want that around 90-95 to promote really good breeding. I separate my babies from my adults so that I can feed the breeders oranges - it is supposed to help - and the babies get mangos, apples, papaya, and anything else.

Won't be long and you should begin to see babies. Good luck!
I just separated and counted mine...I have 25k exsmall, 12k small, and 2.5k medium....hoping a local (to me.. lol.. they are in Reno) petstore is going to start buying them =)