I read the how to and I followed to the instructions and added it until PSI increased by one. Came back a couple hours later and it had increased by 7 to 8 PSI so I backwashed again and it is back down to 14-15. This may be a stupid question, but the instructions said after the first time you will know how much to add so am I supposed to add that same amount every time I backwash or is the first time all I need? I had to buy it in a 25lb box and I didn't know if I was to keep adding it every time until I am out or how much to stop at. Thanks in advance for the replies!