Saturday was a nice, very well lit sunny day. So, I spent about 5 or 10 minutes with my cya test. Doing it over and over again, turning my back to the sun, turning towards the sun, glancing at it, staring the whole time, one eye, two eyes, you name it.
I feel pretty confident I got my eyeball calibrated. The dot was not completely obscured until I hit the 50 mark, so I believe my cya level is possibly around 50 but I'll call it 60, and I thought I would maintain FC levels as though it's 70.
However, there are a few reasons I question that possibility.
A) At the beginning of the season, the pool store said we were at 78 ppm cya. That said, I have had to drain off anywhere from 6-12 inches of water a few times due to excessive rain, and I've also drained about one "step" level a few times during a backwash and topped it back off. Is it possible that I've dropped the CYA level that much through just those small exchanges?
B) My pool seems to be "using" very little chlorine through the day. For example, Tuesday afternoon I checked it to be 11, Wednesday afternoon it checked to be 10.5. (FC levels)
Is that a sign that the CYA level is higher than I think, that FC is being prevented from being used up by the sun?
Or- there are no swimmers in the pool yet. It's also early in the season. Temps have still been fluctuating between cool and warm at best but not hot. The sun is not all that direct during the day yet. With those points, is it possible for my CYA test to be right, and it's just not using that much FC yet with no swimming and summer isn't in full swing yet?
The pool is in full sun. There is no shade over it.