Questions regarding CH and fiberglass pools

[ba67]

I'm getting ready to do a soft closing of my fiberglass pool and I just discovered that all of the rain we experienced lately has lowered the calcium level significantly. The pink water sample turned light purple at 9 drops and turned clear with a pale bluish tint at 14. Does this sound like the CH level is 90 or 140?

I read on here that low calcium can cause staining in a fiberglass pool and can be corrosive to the gelcoat so I assume that I need to add some calcium before doing a soft closing.

Before I add some calcium to our pool, I have a few questions:

1. How high do I need to increase the CH in my pool if my primary purpose of adding it is to prevent staining and protect the gelcoat over the winter? (FYI - We have waterline tile but I try to keep the water below the tiles all winter by draining water out periodically.) Do we need to get it all of the way up to 250-350 like TFP recommends if the pump isn't going to be running for the next 6 months?

2. Should I take any different precautions when adding CH increaser since the water is cold? (Water temperature is 72 degrees currently.) If I have to add 20+ pounds of it, how much should I add each time and how long do I need to wait until I add more. I always add it by broadcasting it in the deep end and brushing afterwards since I don't like to handle a hot bucket of water.

3. What would the repercussions be if I wait to add calcium in the spring and go ahead and close at the current calcium level?

 

[ajw22]

If you have waterline tile with grout then you need a CH level of around 250 ppm. No reason to go higher then that.

Broadcast the calcium on the pool water.

 

[Texas Splash]

The pink water sample turned light purple at 9 drops and turned clear with a pale bluish tint at 14. Does this sound like the CH level is 90 or 140?

Be sure to take the test all the way to the light (baby) blue color.

 

[ba67]

Be sure to take the test all the way to the light (baby) blue color.

The test turned from a light pink to a light purple after 9 drops and then turned clear with a slight blue tinge at 14 drops. Does this mean that the level is 140? I want to make sure I get an accurate CH number so I know how much CH to add to my pool. Also, if I have to add 18 pounds to get up to 250, how much should I add at one time and how long should I wait before adding more? The water is only 72 degrees right now so I worry that the calcium isn't going to dissolve well and will settle to the floor and damage my gelcoat if I add all 18 pounds at once.

 

[Texas Splash]

Does this mean that the level is 140?

Yes, go with the higher number. Red or purple/lavander isn't long enough. You want that light baby blue color to where the drops don't change the solution any further.

 

[Texas Splash]

how much should I add at one time and how long should I wait before adding more?

Best to go in stages as to not over-shoot. If you're at about 150 now, try 50 ppm worth first then re-test in 24 hrs or so. As you may already know, calcium products should be spread across the surface of the deep end of the pool, although many people pre-dissolve in a bucket before spreading as well.

 

[ba67]

I posted on here a few days ago because I had questions about my calcium test results. The test turned a light purple color after 9 drops and then turned clear with a slight blue tinge at 14 drops. Based upon this, I was told by a TFP expert on here that my CH level was likely 140. I wanted to increase the CH to 250 before closing my pool to protect my gelcoat and waterline tile so I added some calcium on Monday. I initially added a 9 pound container of calcium hardness increaser, which should have gotten my level up to 194 according to the pool math calculator. Before adding more calcium, I tested my calcium level3 days later and got a strange result. The sample water turned light purple at 26 drops and didn't turn light blue until 29 drops. I only added enough calcium to get to 194 so this test result cannot be correct. The water sample was 72 degrees with the first test and was only 68 degrees with the second test. Is the cold water throwing off the test results? If so, is there anything that I can do to get an accurate test result? I repeated the test after letting the water warm up for about an hour and got the same result. Reagents are less than a year old and came from TFtestkits.com but have no date on them. I used a speedstir when doing the test. I saw a video on YouTube about metals in the water throwing off the test results but I shouldn’t have any metals in my water since I never use copper based algaecides and don’t have a heater.

 

[Texas Splash]

The CH test is generally predictable when performed as prescribed. To confirm, I use the 10 ml water sample size followed by 10 drops of #10, 3 drops of #11, then slowly add the #12 drops until the solution becomes a light baby blue (no more color change). I multiply that number by 25.

Are you on a well?

Calcium Hardness

A drop-based test that measures the hardness in your water. Once measured, it is used … Read more…

www.troublefreepool.com

 

[ba67]

The CH test is generally predictable when performed as prescribed. To confirm, I use the 10 ml water sample size followed by 10 drops of #10, 3 drops of #11, then slowly add the #12 drops until the solution becomes a light baby blue (no more color change). I multiply that number by 25.

Are you on a well?

Calcium Hardness

A drop-based test that measures the hardness in your water. Once measured, it is used … Read more…

www.troublefreepool.com

No. We aren't on a well. Should I just assume that the calcium that I added increased the CH level to 193 like it should have and add another 9 pounds to get up to 250? I have a feeling that the cold water is throwing off the results somehow.

 

[Texas Splash]

Should I just assume that the calcium that I added increased the CH level to 193 like it should have

I wouldn't make any assumptions at this point. Once the calcium has had a couple days to mix, your CH result should be accurate, so go with your own testing first. While extremely warm water could effect the CH test, chilly water should not.

 

[Texas Splash]

Just to ensure our numbers match, the PoolMath tells me that 9 lbs of calcium should increase the CH by a little over 50 ppm. Is that were you were hoping to see on your end? If you were at 140 before, then 9 lbs should've increased the CH to somewhere around 190-200, coupled with a slight testing variance. Which pool math calculator were you referring to in post #7?

didn't turn light blue until 29 drops.

Oooh wait! 29 drops x 25 = 725. Did you see that? Are you using the 10 or 25 ml water sample size?

If you are using the 25 ml sample size, each drop is 10 ppm, so your CH would be 290.

 

[ba67]

Just to ensure our numbers match, the PoolMath tells me that 9 lbs of calcium should increase the CH by a little over 50 ppm. Is that were you were hoping to see on your end? If you were at 140 before, then 9 lbs should've increased the CH to somewhere around 190-200, coupled with a slight testing variance. Which pool math calculator were you referring to in post #7?

Oooh wait! 29 drops x 25 = 725. Did you see that? Are you using the 10 or 25 ml water sample size?

If you are using the 25 ml sample size, each drop is 10 ppm, so your CH would be 290.

I used a 25 ml sample. If my starting CH level was 140, 9 pounds should have only gotten it to around 195 or so according to the pool math calculator on this site. I don't understand why the test results are showing that the CH level is 290 because I didn't add enough calcium to get to that level. The only thing that has changed from my first water sample is that I added 9 pounds of calcium and the water is a bit colder now.

 

[Texas Splash]

Sounds like your math is correct for a 25 sample, starting at about 140 then added about 50 ppm worth of calcium. We can rule out water temp and apparently your testing & math seem to be good. The only other thing you might check is the droplet sizes. With the TA test I know there can be static electricity interference, so perhaps try rubbing the tip of the bottles (mainly the #12) after every few drops. There's a chance the droplets are coming out too small on that #12 which would result in a higher reading.

 

[ba67]

Sounds like your math is correct for a 25 sample, starting at about 140 then added about 50 ppm worth of calcium. We can rule out water temp and apparently your testing & math seem to be good. The only other thing you might check is the droplet sizes. With the TA test I know there can be static electricity interference, so perhaps try rubbing the tip of the bottles (mainly the #12) after every few drops. There's a chance the droplets are coming out too small on that #12 which would result in a higher reading.

Thanks for all of your help. I just tested my CH again using a 10 ml sample and did what you suggested regarding droplet size. It turned blue at 12 drops, so it looks like it is 300. None of this makes any sense because 9 pounds should have only gotten it to around 190-200 according to pool math. I've now tested the CH level 3 times so I guess I need to trust the test results and not add any more calcium?

 

[Texas Splash]

I guess I need to trust the test results and not add any more calcium?

I agree