Whoa hold on here Meyer and Maria, from what I can remember about Ph is that each species of fish [such as koi or goldfish], has its own very narrow range of Ph preferances anything outside of this will cause health problems even death for our fish .
Nephen you have one half of the equasion there what about alkalinity ?
"Koi and Goldfish prefare a range of 7.0-8.5 Ph nothing higher or lower" ..
It is a fact that high Acidity or alkalinity may cause physical damage to your fish such as damage to gills , skin or eyes , as such prolonged exposure to sub-lethal can cause stress , an increase in mucus being produced also epithelial hyperlasia which is a thickening of the skin and gills, this often ends up with fish mortalities .
Fish also need to maintain their own internal Ph so even small fluctuations of their blood Ph could prove fatal for the fish .
High/Low external water Ph can influence and effect blood Ph which results in either acidosis/alkalosis of the blood.
We should also bear in mind that as well as fish nitrifying bacteria in the filter also have a narrow range of preference between 7.5 and 8.6 Ph.
So in reality the Ph level of 9.0 over a prolonged period will do damage risk alkalosis of the blood as well as cause mortalities
So it has to come down somewhat within the ranges of 7.0-8.5 ph or we may well see further fish mortalities in Johnny's pond .
Johnny can you buy some Microbe_lift PH filterpad innoculat gel and add it to your filter to give it a boost of good bacteria following the instructions to the letter , this will mean stopping and emptying your filter adding the gel to your filter medium whilst no water is in the filter and leave it that way for an hour , then add water to your filter but leave it standing for half an hour before switching your filter on again, the gel makes for rapid colonization of your filter hopefully then everything will drop in place and your Ph etc will settle down making the pond safe for your fish to live in
Johnny I've added a couple of attachments for you and a koi health chart .....as you can see your water is in between baking soda and detergent at this moment in time
Dave