Finally using a real test and super high CYA

[zimdogg]

My FC is down to 7 now. I've put probably 3 gallons of 12.5% LC in the pool today alone. It's super sunny right now, waters crystal clear, no dead algae on the bottom... I'm really confused.

I don't have enough chlorine on hand to keep adding gallons at this rate. Need to get some more and then I can slam tomorrow if I don't pass the OCLT.

Could it be that my CYA is so low that the sun is just burning it off fast?

FC - 7
CC - 0
Crystal clear water

Going to pause this slam, clean my filters, reload on supplies re-check cya, and do the chlorine loss test tonight, then based on results I can either slam tomorrow or do something else. Reasonable plan?

 

[HermanTX]

Could it be that my CYA is so low that the sun is just burning it off fast?

YES. A low CYA will allow the UV to consume your FC.

One way to get an estimate of your pool volume is to take a FC reading. Add a gallon of LC. Let it mix for 30 mins then test again.
Best to do it if with shade over your pool or early evening if your pool does not get shade. Trying to avoid the effects of UV.

So you then you have an initial FC reading at your current pool volume - 12500. The PM app would calculate 1 gal of 12.5% would raise your FC by 10ppm. For example only - your current 7ppm should rise to 17ppm.
Then you do your second test after mixing for 30 mins - Lets say , for example it raised to 14ppm - so you only had a 7ppm increase but were expecting 10ppm. Then change your pool volume number to match the 7ppm increase for 1 gal of 12.5% - for my example that would be 17,500 gals. Just a reminder - this is example numbers only but is one method to try to hone in on pool volume so when you add a chemical you get the expected results.
Note - 1 variable that we cannot control is if the LC has degraded over time due to heat - maybe it is not a true 12.5% but 11% - so this could also affect the test results.

Going to pause this slam, clean my filters, reload on supplies re-check cya, and do the chlorine loss test tonight, then based on results I can either slam tomorrow or do something else. Reasonable plan?

YES.

 

[zimdogg]

YES. A low CYA will allow the UV to consume your FC.

One way to get an estimate of your pool volume is to take a FC reading. Add a gallon of LC. Let it mix for 30 mins then test again.
Best to do it if with shade over your pool or early evening if your pool does not get shade. Trying to avoid the effects of UV.

So you then you have an initial FC reading at your current pool volume - 12500. The PM app would calculate 1 gal of 12.5% would raise your FC by 10ppm. For example only - your current 7ppm should rise to 17ppm.
Then you do your second test after mixing for 30 mins - Lets say , for example it raised to 14ppm - so you only had a 7ppm increase but were expecting 10ppm. Then change your pool volume number to match the 7ppm increase for 1 gal of 12.5% - for my example that would be 17,500 gals. Just a reminder - this is example numbers only but is one method to try to hone in on pool volume so when you add a chemical you get the expected results.
Note - 1 variable that we cannot control is if the LC has degraded over time due to heat - maybe it is not a true 12.5% but 11% - so this could also affect the test results.


YES.

Good stuff... thank you.

 

[HermanTX]

Good stuff... thank you.

One item to add. If you do the test with chlorine to try to hone in on pool volume, then also do it with MA (for pH testing). This then gives you a second set of data to compare. Also, acid does not degrade as much as chlorine may.

 

[zimdogg]

OCLT was a pass.

4ppm FC last night and 4ppm FC this morning
CC - 0
Crystal clear water

My cya test is unknown. I can still glance over the top of the vial and see the dot even at the 30 mark. Barely, but I can see it. I'm calling this 30 since I'm guessing if I were to have a line for "20" CYA, I wouldn't be able to see the dot there and would round to 30.

Having another issue now. Can't seem to get the filter to stop with small water leaks at the gasket. I hosed off the gasket and the areas it seats.. should I have wiped those down? I'm going to try that and see if I can stop it from leaking.

Overall, happy to have no chlorine loss. My initial thought on a plan is to use a couple of the tablets in my auto feeder and keep an eye on FC, then retest CYA when those are dissolved. It's 7am here and my pool is just about in the sun, and will be in the sun for at least 12 hours per day. Full sun, all day.

What should I target for CYA?

Any other suggestions here?

Did all tests again this morning, results below.

 

[HermanTX]

Overall, happy to have no chlorine loss. My initial thought on a plan is to use a couple of the tablets in my auto feeder and keep an eye on FC, then retest CYA when those are dissolved. It's 7am here and my pool is just about in the sun, and will be in the sun for at least 12 hours per day. Full sun, all day.

What should I target for CYA?

Great! Target a CYA of 50. With 12,500 gals, each 3 inch puck of tricolor will raise CYA 2.7ppm after fullY dissolve. So it may take a while to raise CYA to 50. Each puck also adds 4.4ppm of FC.