Water testing for experienced pond keepers Experienced pond keepers check their pond water regularly. This allows taking measures, for instance against algae, quickly and easily, without the need to use chemicals. The sera Koi aqua-test box contains the following test kits: pH valuetotal hardness (GH)carbonate hardness (KH)ammonium/ammonia (NH4/NH3)nitrite (NO2)nitrate (NO3)phosphate (PO4)iron (Fe) andcopper (Cu) Water testing for experienced pond keepers Experienced pond keepers check their pond water regularly. This allows taking measures, for instance against algae, quickly and easily, without the need to use chemicals. The sera Koi aqua-test box contains the following test kits: pH valuetotal hardness (GH)carbonate hardness (KH)ammonium/ammonia (NH4/NH3)nitrite (NO2)nitrate (NO3)phosphate (PO4)iron (Fe) andcopper (Cu)