7.5 is slightly alkaline which is common for UK tapwater. Most fish, even those whose natural habitat is more acidic, will happily tolerate more alkaline water. Fish will undoubtedly be most healthy, happy and in the best condition in water which best matches their natural habitat. It's worth remembering thou that the majority of UK fish are captive bred and have never really experienced 'natural' conditions.My PH is really low. It barely registers on the card. The tap water is around 7.5. What makes it so low and will this be a problem with common community fish? Thanks.