I made my first NaOH solution at a strength of 5mol by following the steps shown in this online calculator:
I used distilled water.
It was all fine for at least the first few days if not a couple weeks, but then I noticed a white crust building up along the inside walls of the clear plastic bottle I have it in, but only above the water line. Then some time after that it seems the NaOH is actually separating within the solution and there are now bits of it floating around in there, with more and more showing up each time I check.
Does any one know why this is happening and what I can do next time to prevent it?