Funny I read it as a 12 year established pond which means its been cycled for 12 years the ammonia build up in the pond has to be some other problem either caused by too many fish high fish load or poor maintenance to both pond and filter lack of water changes etc .
As to the treatment fishygirl take it back to the vendor because its a been used bottle of god knows how long you never use chemical once they have been opened for an unknown amount of time and they should never have sold it to you in the first place basically they ripped you off there .
As to this being funny fishygirl it isnt not when the lives of your fish are concerned its sad
Petco eh ?.... yes we know about them in the UK they have not had good press at all.
Superstore petshops with shop assistants removing dead fish before the store opens each day, maltreating the animals I believe one member killed a rabbit because it bit her "she drowned it" ,cats and dogs from so called puppy farms that die because of lack of injections etc personally I wouldnt touch them with a 10ft barge poll , prefaring instead a koi dealership to buy our koi from but hey each to their own .
Dave