I'm still struggling to get my pond's Hardness up where it needs to be. Thru researching possible corrective actions, such as gypsum, I came across the idea of adding cruched oyster shell to increase calcium carbonate levels.

Has anyone ever tried this, and if so, what were your results?

I ask primarily from a cost standpoint, as 50# of oyster shell is about the same price as 10# of gypsum.

.10 surface acre pond, 10.5 foot deep. SW LA. The epitome of a mutt pond. BG, LMB, GSF, RES, BH, Warmouth, Longear Sunfish, Gambusia,Mud Minnows, Crappie, and now shiners!!...I subscribe!!