Chlorine usage, CYA test and solar cover ..

[Speedo]

After buying the 50ppm CYA solution from TFTestkits (used to show 50ppm CYA in the test), I am now able to verify what 50ppm should look like. This would also explain why when testing inside I get about +15ppm higher than if I test outside (in indirect sunlight).

I was using around 2ppm/day (on sunny days) with the solar cover on. Adding up to 3-3.5ppm FC at night when my target was 5. On a sunny day with bathers (w/o cover, obviously) I could use up to 3.5ppm/day.

I've probably been targeting an FC that's 1-3ppm too high the entire time I've been doing BBB. Obviously the CYA test MUST be done outside with indirect sunlight.

I verified using pool calc that my CYA test was close, using last years level and the amount of water replaced when opening. Of course the difference matched up. Which tells me my testing has always been off.

Now I just need a sunny afternoon to test, hopefully tonight or tomorrow. My guess is I will be using far less chlorine from now on.

 

[jblizzle]

I am not sure I agree with your last statement.

Losing 2ppm everyday in an unused pool is pretty normal (although with the cover maybe it could be lower). And of course with more sun and bathers, the loss will be higher.

So what CYA do you think is actually in your pool now?

 

[Speedo]

Actually the 2ppm is slightly off, it should be about 2.25 average according to my spreadsheet. That's with no usage, covered on sunny days.

After testing the 50ppm solution I've realized that my testing has probably been about 15ppm off. I had a little bit of sunshine in between clouds to play with yesterday, I can still see the dot (just barely) at 30. I need to buy more stabilizer and also wait for a nice sunny day when I can turn my back to the sun and test the 50ppm solution again along with my water and then I will know without a doubt what's accurate.

Most likely I will pickup CYA tonight and assume my current is at 30, start treating as 30+added CYA after 24 hours and then test CYA a week later.

My testing at the beginning of this season seemed to be around 40-45, I had some old stabilizer left over from a few years back that only took it up about 5ppm when it should have been closer to 15. (hence the 40-45 range) Now I'm thinking it could have been 35, but after all the rain we got (in the past month and a half) I probably blew out enough water to remove around 5ppm.