Have him check his pH first. Too high 8.5, Too low 6.5, WH can't take up
the food it needs.

I found my box at a Farm & Garden (Farmer's Exchange) HD didn't have it,
nor any other hardware/garden shop. ~ jan

I knew there was something you could add but since I don't use anything in
my pond I wasn't sure what, or how much.
Where can he get this potash from?
Would Home Depot have it?
Patty
(Do you know where your water quality is?)