thanks Sandy and Jorge, I did notice the p.o. is more expensive. So far I have used the sodium citrate. I put a larger humidifier in the room so I can get the humidity up to 60%. I would like to try to cut the clearing time a little. Using the 3% citric acid solution I have been clearing for 4 minutes. I have not had any stain on the unexposed coating so I thought I would try reducing to 3 minutes. How will I know when the clearing time is inadequate?