We bought a lovely country home on the edge of Bodmin moor three years ago. In centre of garden is a swimming pool sized pond full of carp. At our last home, we had a natural, deep, self filling from rooves and filtered out through gravel beach pond full of frogs and goldfish etc. The koi in our pond have been there at least 16 years, we had problems with green water and fish eat any greenery that tries to grow such as water lilies and irises. Sorted green water but now larger fish are found floating with milky discharge coming from their mouths. Had water tested and advised we need a KH buffer, costing about £100 or so. Could someone tell me what a KH buffer is and what it does?