Just for reference, Smith Creek Fish Farm sells Alum by the ton for $1398.99. Using that number Alum is 8.74 times more expensive to apply than gypsum in my area. My results show gypsum to be 2/3rds as effective as alum, making it a no brainer in my situation. Just trying to save some people some money while avoiding the PH issue regarding fish kills. Which I believe Lusk's crew ran into in the beginning when he had to replace a customer's fish...an old story told during a Pond Boss convention back 20 years ago.