CYA issues

[deenamccauley]

We have a very busy semi public pool. Full Southern exposure.
Approx 100,000 liters
I added 3000 grams 100% CYA May 6, did a reading about 10 days later and it was maybe 20 ppm.
Did a reading middle of June and as far as I could tell it was 0. So I added another 800 grams CYA.
Tested again yesterday and I still am maybe getting a 10 ppm reading.
Am I just inept at reading this or have I just not added enough.?
I am going through about 40 litres 12% chlorine a week, which is literally the same as last year.
Does that seem about right for this size of pool.? I don't want to overdo it because we went through that one year too, not fun.
Any suggestions, greatly appreciated.

FC 4.4
CC .2
Alk 90
PH 7.3
CYA ???
CH 200
Water temp 28 C

 

[JasonLion]

Each 1000 grams should raise CYA by 10, assuming it is 95+% cyanuric acid. The test is +-10 at best and often more like +-15, and it will often read values below 20 as if they were zero, so don't expect the test to exactly match what you put in.

CYA will go down over the course of the season. How much it goes down depends on several factors, the amount of water splashed out, if you backwash and how often, any water that is drained out of the pool (overflow?), leaks, and so on. If your pool is getting a lot of use or has a leak, the CYA level can go down fairly quickly.

If you are testing with the Taylor disappearing black dot test, I would add more CYA till your level comes up to at least 30, preferably a little higher. If you are using test strips, I would not trust them at all and get a real test kit.

 

[deenamccauley]

I'm testing with the Taylor black dot. Yes, we do get a lot of splash and need to backwash every 3/4 days.
We are topping up the pool every day usually about an inch so we do go through a lot of water in that pool.
I'll add some more CYA then. Just didn't want to be over doing it if I was just having issues reading the test.
Thanks for your help.

 

[bluskyguy]

I've been told when you add CYA (Directly to skimmer) you can't backwash for 5 days. I do have a SWG pool.

 

[deenamccauley]

That is a big part of it too, we just CANNOT go very long without backwashing so I know we are fighting a losing battle.
Because we are basically a public pool we never close, so we get lots of use which means lots of Crud in the filter, so lots of back washes.
I actually put my CYA in a knee high nylon and suspend it from a chair leg....down over the pool eyes. It will dissolve about 400 grams over eash eye overnight.

I've been told when you add CYA (Directly to skimmer) you can't backwash for 5 days. I do have a SWG pool.