Do the Member's Mark Tabs have stabiizer?

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
I just got the TF-100 test kit. My CYA also reads 100. I also use the Members Mark tablets. How much water should I drain to get it in the proper range? Then do I switch to liquid bleach? Thanks.
 

jblizzle

Mod Squad
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May 19, 2010
43,238
Tucson, AZ
:wave: Welcome to TFP!!!

All trichlor tablets add CYA to the water, in addition to the chlorine they are also very acidic and will drive down pH and TA.
Your CYA is already too high and would warrant a 50% water replacement and then stick with bleach.
Follow the FC/CYA Chart to know how high you need to maintain your FC as a function of your CYA

 

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
I drained 14" out of the pool and am now starting the refill. I removed the Members Mark tablets from the chlorinator and bought the liquid chlorine from Walmart. How do I know how much liquid to add? The gallon jug says it is 10% Sodium Hypochlorite. Before I drained the pool the chlorine was a 1-1.5 and the CYA was 100. ph a touch low at 6.8 but I'm expecting the new water to bring that up a little. Thanks.
 

jblizzle

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May 19, 2010
43,238
Tucson, AZ
So you probably are replacing 25-30% of the water then. That will lower your CYA to 70-80ppm. You look at the FC/CYA Chart for your CYA level and pull the target number off of it. Enter your current FC readings into PoolMath or the old web-based version of PoolMath. Enter your target FC level. Enter your bleach strength. Make sure your pool volume is set. And it will calculate how much bleach you need to add.
 

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
Thanks. Is there a more precise way of calculating pool volume? The pool was here when we bought the house. Pool maintenance guy once said around 18000. Also, If I stop using stabilizing tablets how long does stabilizer to dissipate? Rain and routine manual top offs should help too. Here in Houston I add at least an inch a week.
 

jblizzle

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May 19, 2010
43,238
Tucson, AZ
CYA will generally only be reduced by replacing water. It will slowly breakdown in very warm sunny climates to the tune of 5-10ppm a month in the summer.
Topping off water that evaporated will NOT lower the CYA level in your pool.
If you get enough rain in the water where you need to pump some of the water out of the pool, that will reduce the CYA a bit because you are pumping the water out.

You can get a general idea of the volume by seeing if you consistently over or under shoot your targets when adding chemicals using the PoolMath outputs.
Just pick a number to start with and track your testing and chemical additions.
 

mknauss

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May 3, 2014
23,297
Laughlin, NV
Start with the 18000 gallon figure. As you test and add chemicals we can explain how to narrow it down.

Stabilizer (CYA) is removed by removing water with it in it from the pool. So evaporation does not count. Only if you drain some water before a storm (or the storm is big enough you get a lot of overflow) will the CYA be impacted. It will degrade a few ppm per month in the summer.

So you will need to either manage your pool with your high CYA, or drain again, down to leaving 1 foot of water in your shallow end, and refill.
 

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
Thanks for all your advice thus far. As predicted my CYA dropped to 80. I've added liquid pool bleach at 10% concentrate to bring the FC up to 7.5. ph still at 7.2. My CC was 0. (after testing FC for above 5.0 via the TF-100 instructions, the solution went back to clear after the 15 drops of 003). I brushed the pool this morning to get rid of any lingering algae on the sides. The pool is mostly clear and nice looking. will an FC of 7.5 be an eye irritant? Any other suggestions?
 
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mknauss

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Bronze Supporter
May 3, 2014
23,297
Laughlin, NV
At your CYA of 80 ppm, you will not even notice the FC level up to SLAM level of 31 ppm.

Eye irritants are normally CC, out of range pH, and rubbing your eyes too much in the pool (kids mostly).
 

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
I thought about starting a different thread but this is a continuation of my stopping using Members Mark tablets and my switch to liquid bleach. On Wednesday I added 10% liquid chlorine to bring the FC to 7.5. With a CYA of 80 I thought I was close to the right amount. Today, Saturday, I once again checked the FC level and it was a 1.50. My thinking was that if I have a high CYA number, thus a high level of stabilizer remaining in the pool, then my chlorine would not dissipate that fast. Since I am accustomed to a chlorinator that I checked once a week how often must I now check chlorine levels using liquid bleach?
 

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
I am testing the chlorine about every other day. I notice that the liquid chlorine dissipates quickly even at a CYA of 80. After a few daily tests, I thought I could just add a few cups of chlorine a day and stay in my 7.0 range. I tested this morning and I was back around 2.0. Is it normal to have to add almost a gallon/day with a CYA of 80? I know the 80 means I am keeping a high amount of FC but doesn't that also mean I have a lot of stabilizer in the pool and thus should not dissipate the chlorine as fast? I bought 6 gallons of 10% pool chlorine from Walmart around 8 days ago and I have 1 left. Thanks.
 

mknauss

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May 3, 2014
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Laughlin, NV
Your pool will lose 2-5 ppm FC per day at a CYA of 80. You still need to add liquid chlorine every day to make up for that loss.

Not quite a gallon a day of 10% would not be unusual.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
23,297
Laughlin, NV
Not really. It could lessen by ounces, but maybe not. No matter what, you want to work your CYA down to 50 ppm by the fall.
 

Glofton

Well-known member
Jul 3, 2018
62
Loganville Ga
Thanks for all your advice thus far. As predicted my CYA dropped to 80. I've added liquid pool bleach at 10% concentrate to bring the FC up to 7.5. ph still at 7.2. My CC was 0. (after testing FC for above 5.0 via the TF-100 instructions, the solution went back to clear after the 15 drops of 003). I brushed the pool this morning to get rid of any lingering algae on the sides. The pool is mostly clear and nice looking. will an FC of 7.5 be an eye irritant? Any other suggestions?

You mentioned algae, have you done an OCLT? Maybe thats where some of the FC is going...may need to SLAM.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
Realistically, if you lowered your CYA your daily FC losses would be higher meaning you would have to add more bleach everyday. For example at your current CYA maybe you're losing 3 PPM of FC everyday, but if you lowered the CYA you might be losing 3.5 PPM of FC everyday.

The daily losses are mostly due to sun exposure so the only way to reduce that would be to cover your pool. And the amount of bleach required is a function of your pool volume so the only way to lower that is to make your pool smaller :)
 

Rick T

Well-known member
Apr 28, 2019
105
Houston, TX
At $4/gal including tax from Walmart is there a cheaper solution for liquid chlorine? At that rate I'm over $100/month in chlorine alone. My chlorine tablets used to cost about $200-300/year. Is there a non-stabilized (no CYA) chlorine tablet available? I still have a 3/4 large bucket full of tablets but didn't want to use them for fear of bringing my CYA back up.