Most ash from burning wood consists of potassium hydroxide. It can be caustic and react with soluble nutrients that are in the water column. Most potassium bonds are very strong and will need to be broken by drastic PH change or the light acid produced by plants roots.

There is very little phosphorus or nitrogen in wood ash. Mostly potassium and calcium with other micro nutrients but most all in the caustic side of PH.

My petrochemical advice is that it will work fine to tie up excessive acidic nutrients that are soluble in the water. Like every thing it can be over done so check PH. If the PH is high it may do little to nothing.

IF you are lucky that there is a lot of soda ash or calcium carbonate this will act as a PH buffer holding soluble PH to 7.2


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7/8th of an acre, Perch only pond, Ontario, Canada.