1st thought - bad test kit (testing other water samples will eliminate this factor, test some bottled drinking water, distilled water, water with some baking soda added etc to see if you get different results)
Are you testing the aquarium water or straight from the tap? If the aquarium has been running for awhile it should be all gassed out but if straight from the tap trapped gases could be an issue.
Does this "cloudy" water clear from the bottom first and possible you can see bubbles popping at the top? My water has air injected into it to help my iron filter remove the dissolved iron so when the water comes out it is "cloudy" and it is "air" not CO2 or oxygen per se.
A picture is worth a thousand words. Something might stand out to us that you might not have thought to mention.
And I realize we haven't answered you're original question yet but once we figure out the actual problem (why the pH is so low) we can help with it appropriately.