CYA Stabilizer Dropped from 30 to 20 Overnight?

[ellemgee]

I added a gallon of CYA stabilizer for the first time ever at around 4pm and then tested at 10:30pm last night and got a reading of 30. Tested again this morning just to double check and got around 20. Does that make sense? Do I need to keep adding stabilizer to get closer to 30 again? Will the level of CYA drop that much over night? (Unless, of course I did the first test wrong, but I did double check it a few times and it looked like a clear 30).

If it matters, my FC has been all over the place. I am attempting to hold my CYA and FC levels steady enough to SLAM/shock my water so that I can clear up the cloudiness and finally get it suitable for swimming!

 

[pinguy]

What was the level before you added CYA?

In a 15,200 gallon pool, 1 gallon liquid stabilizer will raise CYA by 24.

In my experience it can be really difficult to test a 10ppm difference at the low end of the CYA test.

 

[samt]

You tested too soon, stabilizer takes a while before it will test correctly. I always sneak up on it by adding a little and testing 5 days later. Be slow with that stuff! The only way to lower is to drain and replace.

 

[pinguy]

You tested too soon, stabilizer takes a while before it will test correctly. I always sneak up on it by adding a little and testing 5 days later. Be slow with that stuff! The only way to lower is to drain and replace.

OP used liquid, which shows up on the test much faster

 

[samt]

OP used liquid, which shows up on the test much faster

Ok, sorry my bad.

 

[ellemgee]

To answer questions:

Level before adding was 0 (or else less than 20 and undetectable with the test)
Yes, I added liquid stabilizer, which the bottle billed as "instant" but I still tested a few hours later.

Okay, so I should have basically expected by level to rise to about 20 (or 24 from what one of the replies said)... so add about another half gallon and I should be to 30? Is that what seems like the right thing to do? I don't want to over add and I also don't want to waste money on stabilizer if it's not totally necessary. The pool is nearly full sun all day, so it really gets a ton of sunlight all day. Thanks again to everyone who responded.

 

[basod]

You probably want to shoot for the high end of 30-40 range being in full sun.
Without it your FC will deplete rapidly.
The CYA will drift up with evaporation, and go down if you have a lot of rain & backwash/refill regularly.

 

[jblizzle]

Lighting is a lot different between 10:30 PM and in the morning.
Plus the test is only good to +/- 15ppm or so anyway.
You are in the noise.

 

[ellemgee]

Okay, I tested again. Again, got around 20. Gonna add another gallon then and hopefully be able to get it up to the 30-40 range and get it to stay there. Also, maybe this is a dumb question, but I hear people talking about backwashing a filter, which can lower CYA levels. Can you backwash a cartridge filter? I'm assuming I will loose some CYA when I clean the filter (spray it out with the hose), but is this the same thing?

 

[basod]

You don't wash cya off filters. When you remove water from the pool and add fresh water either through hose or rain you've diluted the cya that you've originally added. It's chemical that will never leave your water unless you have the special soil bacteria that can consume cya when your pool is winterized. That is extremely rare

if you lower water level when closing and refill on opening expect to add a small amount of cya to get back to target range

 

[ellemgee]

You don't wash cya off filters. When you remove water from the pool and add fresh water either through hose or rain you've diluted the cya that you've originally added. It's chemical that will never leave your water unless you have the special soil bacteria that can consume cya when your pool is winterized. That is extremely rare

if you lower water level when closing and refill on opening expect to add a small amount of cya to get back to target range

Great! Thanks! That's what I thought!

 

[pooldv]

What you have read about not backwashing after adding CYA refers to people who add granular stabilizer directly to the skimmer. The CYA granules then get trapped in the filter and can take up to a week to dissolve. If you backwash a DE or sand filter before it dissolve s then the CYA gets backwashed too. This does not apply to liquid CYA. No, you can't backwash a cartridge filter but if you clean the cartridge before the granular CYA dissolves it will be lost. We recommend adding it in a sock to dissolve to avoid this problem.

Are you using Poolmath to calculate your CYA dosage? It seems like you are unsure of how much CYA you are adding and how many PPM it should add. Poolmath will tell you exactly how many ounces of CYA to add to achieve your target CYA ppm. Link to Poolmath is up there ^^^.

 

[ellemgee]

Are you using Poolmath to calculate your CYA dosage? It seems like you are unsure of how much CYA you are adding and how many PPM it should add. Poolmath will tell you exactly how many ounces of CYA to add to achieve your target CYA ppm. Link to Poolmath is up there ^^^.

Yes, I am using Pool Math, but I was surprised that the test results changed so much from one day to the next. I just assumed I would get 30 every time I tested after adding the initial batch of stabilizer. But based on other replies it seems like this is a normal thing. I'm going add more liquid stabilizer (assuming the level is at about 20 now) to get up to the 30-40 range based on what's recommended by Pool Math. I didn't realize that the test sort of varied on the low end like that. Just wanted to make sure that I wasn't doing something wrong before spending more money on stabilizer and then possibly sending my levels up too high if it was just a user error.