using shock, liquid chlorine question...

[eugchen]

hi guys, newbie here with some questions....

i did use chlorine tablets for about a year, and it raised my CYA quite a bit to around 130. emptied about half the pool with water and now CYA around 80 or so. SLAM levels 31 and FC levels to maintain are 9-11. FYI, my family really doesnt use the pool very much. i know its a shame, but we arent huge pool people and basically inherited the pool in this house.


i finally recently got on board with the tfp method. had a bout of algae and went through SLAM to get rid of it and now maintaining FC levels. so now im trying to keep FC around 10.

1. what i have been doing for the past few weeks is adding a gallon of liquid chlorine and raising FC to 15-16, then every 3 days, FC goes back down to 10, and i add a gallon again. IF FC ever got to lets say 5-6, would algae form immediately in my pool? or not necessarily, and i should just try and keep FC at least 10 or above?

2. how do people around use tablets? doesnt CYA just go up? do people drain out some of their pool once a year or something?

3. ive been reading about shock, raises FC up quite a bit? been reading there are two main kinds, cal-hypo and dichlor. dichlor raises CYA so not ideal for me. would cal-hypo be something good i should use once a week to get FC levels real high?

 

[DrewLG]

i did use chlorine tablets for about a year, and it raised my CYA quite a bit to around 130. emptied about half the pool with water and now CYA around 80 or so. SLAM levels 31 and FC levels to maintain are 9-11
....

1. what i have been doing for the past few weeks is adding a gallon of liquid chlorine and raising FC to 15-16, then every 3 days, FC goes back down to 10, and i add a gallon again. IF FC ever got to lets say 5-6, would algae form immediately in my pool? or not necessarily, and i should just try and keep FC at least 10 or above?

Not necessarily, especially now that your pool water is probably very cold. But in the summertime, you'd be asking for trouble by allowing FC to fall below 6ppm with CYA at 80ppm.

Ideally, you'd maintain FC at a steady, constant level right at your target -- a saltwater chlorine generator or an automated liquid-chlorine dispenser will do that. But if you're manually pouring liquid chlorine and can't do it every day, it's fine to overshoot your target FC concentration and then let the level drift down over 2 or 3 days. Just remember that the FC loss rate will vary with the seasons, bather load, amount of debris being blown into the pool, etc., so you won't be able to count on a steady 2ppm/day loss all year. It could be much lower in the winter and much higher in the summer.

Also, be aware that the phenol red pH drop test starts to become inaccurate (it reads higher than it should) as FC concentration rises above 10ppm. So if that's the pH test method that you use, you may want to lower CYA to 60 or 70 in order to get your target FC concentration below 10.

2. how do people around use tablets? doesnt CYA just go up? do people drain out some of their pool once a year or something?

They drain periodically (or they live where they get so much rain that the pool drains continuously), and/or they throw a pound or two of powdered chlorine "shock" into the pool once a week to temporarily keep the algae at bay, and/or they use algaecides (maybe deliberately, maybe unknowingly as a component of a pool-store magic potion). Regardless of what they do to keep algae from becoming too visible, though, their high CYA may prevent them from having enough HOCl constantly present to keep the water sanitized.

3. ive been reading about shock, raises FC up quite a bit? been reading there are two main kinds, cal-hypo and dichlor. dichlor raises CYA so not ideal for me. would cal-hypo be something good i should use once a week to get FC levels real high?

Cal-hypo raises calcium, which doesn't dissipate and is bad for your pool and equipment at high levels. If you're always keeping your FC at or above the target level for your CYA concentration, you don't need to regularly shock with anything.

 

[Mdragger88]

To elaborate more on the “shock” (cal hypo/dichlor) vs liquid chlorine - they all do the same thing fc wise if used in equivalent amounts. What’s different is their other effects. None of them are more “magically effective”.


Generally, even at today’s high prices, liquid chlorine gives the most fc for the $ & the least undesirable side effects. The only better option is a salt water chlorine generator.
In LA you probably have enough ch already (you didn’t list your current ch level or your fill water ch)
so it’s possible adding more calcium is not recommended. If you want more fc add more liquid chlorine. Simple.

 

[eugchen]

thank you. that chart is awesome. will save it for myself!

 

[eugchen]

one addition question, on that left side of image, when you add 1 gallon of 10% chlorine, im noticing that my FC only increases around 5ppm. i think my pool is between 13-15k in size. so your image shows 15k. FC is about 1 month old, and stored indoors. im checking FC before adding, then add liquid chlorine in evening, running pump for 30 min, then checking FC again. what could cause this?

 

[Mdragger88]

Either your liquid chlorine isn’t as potent as listed or your pool volume is larger.
I used
PoolMath effects of adding in the the hamburger menu.
Next time you use acid to lower ph follow up with a subsequent test 30 minutes later and see what you get. If its a little different then than what poolmath figured adjust your volume in poolmath accordingly. Muriatic acid doesn’t suffer from degradation like liquid chlorine so it’s a helpful metric.

 

[eugchen]

ok so you mean check ph before acid, then add 1 gallon of acid, wait 30 min, test ph again and see where ph goes to? That will tell me the gallon size of my pool?

 

[Pauls234]

That's the correct concept, but not a full gallon! Acid doesn't degrade in strength the way liquid chlorine can so what she's suggesting will isolate the pool volume variable. If your results are NOT as expected that points to pool volume estimation being off. If in line then the LC had degraded some.

 

[Mdragger88]

Only add what
PoolMath says to add - very unlikely that’s a whole gallon. Check ph again in 30 minutes or so & see where you landed- make note if you’re over or under your calculated mark. Keep dialing volume in that way.

 

[eugchen]

is it true that if ph is too high, i.e. 8.3, chlorine will be less effective in killing pathogens?

 

[mknauss]

Only if you have 0 CYA.

 

[eugchen]

Ok guys so i did the muriatic acid test. tell me if this makes sense. kinda odd data.

i took pool water to Leslies today (i know, i know) and here is what they found.
FC 15ppm
ph 8.2
TA 82
CYA 81
calcium hardness 194

then i came home and checked myself and got the following
FC 12ppm
ph 8.2

concerning FC, i believe my data since i added a gallon of FC 2 days ago and it was around 15 at the time, so 12 makes more sense today.

concerning the ph, i added 0.5 gallon of 14.5% muriatic acid to the pool (8 cups, measured precisely). ran pump for 40 min, then checked again, and my ph went down to 7.2!

according to pool math, my pool is 8000 gallons? i dont think that is right.

if my pool was 8000 gallons, 1 gallon of FC 10% would add 12 and it definitely doesnt do that. its around 5-6ppm added.

 

[Mdragger88]

Ok guys so i did the muriatic acid test. tell me if this makes sense. kinda odd data.

i took pool water to Leslies today (i know, i know) and here is what they found.
FC 15ppm
ph 8.2
TA 82
CYA 81
calcium hardness 194

then i came home and checked myself and got the following
FC 12ppm
ph 8.2

concerning FC, i believe my data since i added a gallon of FC 2 days ago and it was around 15 at the time, so 12 makes more sense today.

concerning the ph, i added 0.5 gallon of 14.5% muriatic acid to the pool (8 cups, measured precisely). ran pump for 40 min, then checked again, and my ph went down to 7.2!

according to pool math, my pool is 8000 gallons? i dont think that is right.

if my pool was 8000 gallons, 1 gallon of FC 10% would add 12 and it definitely doesnt do that. its around 5-6ppm added.

Leslies uses “adjusted” ta which is actual ta - some cya.
so if you put their ta number into poolmath for your calculation then you may have added the wrong amount of acid as the higher the actual ta the more acid is required to lower ph by the same amount. Use your actual ta measured by your test kit when calculating acid additions in
PoolMath

 

[Mdragger88]

There’s a simple volume calculator at the bottom of this page

PoolMath

Discover the calculator behind the perfect pool, PoolMath. Dealing with pools has allowed TFP to become the original authors of the best calculator on the net.

www.troublefreepool.com

And this one is more in depth

Pool Volume Calculator

Check out Pentair's easy-to-use pool volume calculator to calculate the volume of your swimming pool water by choosing the shape, dimensions and depth.

www.pentair.com

Hopefully between the two you can get a closer estimate

 

[Pauls234]

Ph test is invalid if FC is over 10ppm. It reads a false high so need to let fc drift down before doing this exercise

 

[JoyfulNoise]

You really can’t use pH to check your pool volume. It’s sensitive to too many variables and PoolMath only gives an approximation of pH for SMALL VARIATIONS in pH (only accurate when changes are +/-0.2 units).