Stabilizer testing is very subjective, and there are a lot of things that could give you different readings. For example, if they're testing via turbidity test, having algae in the pool will usually give a higher than accurate reading. If you're using strips, then shock levels of chlorine can bleach out the test, giving a lower than accurate reading. Depending on how bad your algae problem is, the algae could be degrading the CYA that's in the water, causing the levels to drop.

My advice is to buy a drop-based kit, test it yourself, and dose your pool accordingly. I wouldn't do anything based on strip testing.

Janet