Why is it going back down?

As you can see I’ve kept a very close eye on my LH levels and each day seems to get a bit darker. Today I’ve had my highest number/darkest line but within 6 hours it’s going back down. Could this depend on the concentration of the urine or am I crazy? Plan on doing the BD tonight in the next hour or so when hubby gets home but I’m confused what causes the numbers to fluctuate so much.