Well, you must get an accurate CYA reading for sure. But you can't test it indoors. You must be outside on a sunny day, sun at your back. That's a must. So try that again tomorrow and if needed, pour the solution back & forth and re-try the test as much as you need to. The CYA is the foundation of the proper FC level, not the other way around. And if you suspect the CYA is below 30, it "may" actually be much lower since those tubes only go down so far in numbers.
As for FC loss, if you are experiencing an FC loss of more than 4 ppm in a 24 hr period, algae is suspect .... or there's not enough CYA to protect your FC during the day. You can always do an overnight (OCLT) test to rule-out the algae, then you know it's just a matter of increasing CYA to at least 30, maybe even 40 in your area as it warms-up.