I've no idea I'm afraid, but it might be sensible to consult a good petshop or garden centre where they sell fish and other supplies.

thanks :)

hello, what makes you think the water is to acid, and how are the koi reacting to this ?

yes some fish have died over the weekend, my friend has had the water tested and has been told it is to acid
she was told to buy some crushed coral??? to put into the water to help bring the water back to the corect balance.

hello, as bamboo suggested go to an aquatic centre and buy a water testing kit, these are not very much and you can test your PH and usually nitrate and ammonia levels, they have very easy instructions of what to do,if at all possible you need to do a partial water change with clean water, if possible not directly from the tap but instead fill a water butt and let it stand overnight then use it, tap water PH is usually about PH. 7 ( it is in wigan ) so really thats what you are aiming for,try and obtain some crushed oyster shell from the same aquatic store this acts as a decent buffer against PH swings, "have fun"