Weird ph readings

[kansei]

First its an est. tank (125 gal ) with ammo 0 (API)nitrite 0 nitrates 20(nutrafin) , weekly 30% water change with gravel vac ( python) Gh 20 (1+1 drop) kh >20( 1 drop chage to yellow) with a nutrafin hardness test . When I check my ph with API test I get 6.4 when I test with nutrafin test I get 5.5 , my tap water tests 6.8 , 5.5 respectively . All tests are liquid regent . I bought the nutrafin test as it was wide range and I wanted to make sure the API was not just bottoming on the range (6.0 ) . All tests are ok by the date on packaging , anyone ever have this happen.

 

[TomK2]

Wow. It is rather common for water as soft as yours to have a pH below 7, but I have no explanation for why the kits differ by so much. I find the reading of 5.5 to be a little hard to beleive.

 

[kansei]

I do to , as I think it would be close to being acidic enough to erode at things . I just don't understand such a differance between two kits . The nutifin kit says it wide range 4.5 to 9 and the API kit only reads 6 to 7.6 .