Got a crystal-growing kit for Christmas. I have three sealed bags of solution that is supposed to be 80% water and 20% Phosphate. All three have lots of hard crystals in them. I'm assuming they should be liquid. Can I just heat the bags gently (in a bowl of hot tap water? In the microwave?) to make the phosphate go back into solution?
What caused them to form crystals prematurely? Cold? Physical shock - jostling?

The solubility of phosphate depends on the temperature. And since the solutions in those kits are saturated, you would get crystal grows with lower temperatures or if a little of the water evaporates. You can heat the bags gently and mix the content. If the crystals are really big, just crush them and mix well. Try to heat only a little at a time. If you heat a lot, crystal formation will be really fast when it cools down and they won't be very pretty. You could also just add a little water.