Camo, a 1.5 acre pond will need about 7 ton of gypsum to have any effect. Gypsum and lime are very slow to dissolve and act. I would suggest 10-15 tons of AG LIME, It runs about $10 per ton delivered and spread. You can NOT use too much ag lime and it will have long term benefits in your neck of "Green Country".

I live in St. Louis and could help you if you need to use alum. Just send me a PM.