Use distilled water that has been freshly boiled for at least 5 minutes to insure solutions are carbon dioxide free. This step is very important . You will know when it is all dissolved by the solution turning clear.
Some workers recommend centrifuging before use.
In any case, it is good practice not to use any of the staining solution from the bottom of the vial. Usual staining time is 1-5 minutes. We can not over emphasize the high sensitivity of this stain to carbon dioxide. To avoid precipitation, make fresh staining solution each time. Keep staining times short and always rinse in carbon dioxide-free distilled water.