Well, I have exactly the same problem and I'm in the process of a SLAM. I always wondered if it was bushfire related. But I think the consensus is no, it's algae, but could have been triggered by the ash. In my case, I didn't know about TFP so I didn't have proper CL levels. I wonder if the ash brought in lots of phosphates, which means with poor CL management, algae.
Regarding the test. I'm new too, but what I did was I went to the pool shop and then played with the kit hours later on the same sample. This allowed me to get comfortable with the levels. Especially CYA. From what I can tell, you have to just NOT see the black part of the flask. That is what put the level at par with my pool shop. Even when I didn't think I saw it, I looked down the top and realised I just could.
Regarding the other tests, suspect that my CA test was wrong. In my case, it was consistently 25% over actual value, including the reference sample. I've emailed Clear Choice to find out if this is normal. All other tests closely matched my pool shop.
I'm on day 2 of SLAM and the brown stuff still comes on my pool floor every 4 hours or so. I scrub, run vacuum robot, and backwash twice a day. The white milky liquid is intense. So I'm assuming this is a good sign. My CL consumption is about 4ppm per day, however, today is 30 in Sydney, so who knows how much is also because of the weather.