pH testing problems! City of Ottawa tapwater tester said 7.6, Fluval test 5.5!

[Tamaradebra]

Hi, this all started at Critter Jungle. i brought in my water sample due to dying plants and they said the problem is pH, too acidic .Measured water at 5.5 with Fluval master kit for professionals (big briefcase style). My API kit said 7.0 but it was just expired so I threw out the whole thing. I bought a $50 new Fluval home master kit which also said 5.5, tests up to 9.5. So I got the City to come test the tap water which was at 9.23 at 6.1 celsius and aquarium 7.66 at 26.1 celsius. I bought a stick on Seachem pH colour wheel which seems much more accurate. But what do I do with the Fluval kit and why isn't it working?! Fluval's website is down. This feels so crazy! A shrimp breeder I met says my new Fluval substrate/stratum is what keeps lowering the pH but it doesn't solve the mystery of inaccurate testing. Please any help or shared experience appreciated.