Hi guys. I have tried to test the CYA a few times with my TF-100 kit. I can ALWAYS see the black dot in the bottom of the tet tube and I KNOW thre is CYA in my pool.
I have done this test after the CYA has been in there for at least a week. Furthermore I know there is CYA because the chlorine is holding. What am I doing wrong ?

How high do think the cyanuric acid is?

If he is saying the black dot does not seem to go away, would that mean it is too low?

With the CYA test, it can be difficult to get a precise reading, but the test is very reliable about giving a rough answer. If you can still see the black dot even when the tube is completely full then CYA is 20 or lower. This result is normally called a CYA of zero, but that doesn't mean CYA is exactly zero.

Here is a brief review of the procedure: mix equal amounts of pool water and CYA reagent (normally done in a mixing bottle with the levels to fill to already marked). Mix for at least 30 seconds, longer if the pool water is cold. Pour into the view tube until the black dot disappears.

You can cross check the CYA test result with what percentage of your FC level you lose over the course of a sunny day. With CYA around 20, most pools will lose more than 75% of their FC level over the course of a sunny day. The amount lost varies quite a bit depending on just how much sunlight reaches the pool, so this is only a rough guess. Still, if you are losing say less then 50% of your FC level in a day, something is going wrong.