Is my FC consumption reasonable?

[Water_man]

Hi all

It’s been almost two weeks now that I’ve been using what I learned here, including having meaningful
data of water testing (Taylor K-2006) and not just meaningless OTO and inaccurate strip tests as it was done in the past.

Unlike the “good old days”, when the “stabilized chlorine” tabs and the weekly 5 – 10 ppm shocking were assumed to be doing the job, now I know exactly what goes in and what’s going on inside.
I just wonder if my daily consumption of FC (see below) is normal. Once I know what to expect I will check FC every other day and I’m not planning to post another question on this topic unless something unusual happens.

Here’s the “chlorine history” of my pool.

I opened a “green pool” on Friday, May 16. This will be assigned as “Day 1” in the table below.
I shocked with bleach to 20 ppm. CYA pool store reading was 56. On Day 6 my Taylor kit arrived and I measured CYA 60.

On Day 3 I did another 20 ppm shocking with Ca Hypo. I chose it because the sinking granules took care of the brown spots on the stairs (an advice from another New Englander who also opened a “swamp”.)

Day 1’s pH of 7.9 was gradually adjusted to 7.5. CH was gradually adjusted from 170 to 230.
between day 6 and 9.
Alk was tested 140 solid between Day 6 and 9.

Here’s a table of the FC levels. CC has always been < 0.5 , although it hasn’t been zero.

I’ve been using Chem Geek’s table for maintaining a minimum FC of 5 and targeted 6.8 , according to my CYA 60 level. The amounts of added 6% bleach and Ca- Hypo were calculated using the Pool Calculator.

The “Treatment” in the table refers to treatment applied following the water testing.

Day # ... FC ....Treatment ...................Notes

1......................... 20 ppm bleach............ Green pool
3......................... 20 ppm cal hypo..........No green present.
6 ............7.5....... 1 lb dry acid................ Pool almost 100% clear
7............ 7 ...........1 lb dry acid................ Pool 100% clear
8 ............5........... 8 Oz Ca Hypo
9 ............5
10 ..........? ............8 Oz Ca Hypo ............Solar cover installed. Heater on.
11.......... 5.5........ 84 Oz bleach
12........... 6
13........... 4 ..........1 Gal 2 Oz bleach

So, if my CYA is definitely not low, and the CC present is always <0.5 why am I losing FC, and is the lose rate reasonable?

As an ex- user of the traditional stabilized chlorine method, I can’t escape comparing the chlorine utilization then and now.

When I used that method during the last two seasons, two 3” &quot;stabilized chlorine&quot; tabs lasted for about 4-5 days and the elusive “total chlorine” OTO test showed a consistent 2-3 ppm level.

[aylad]

I'm assuming that the FC levels you show in your chart are residual before you add the "treatment" for that day? If so, what was the peak FC after the treatment?

I have a 29K gallon vinyl IG pool in full sun all day in Louisiana, and I find that if I don't keep my CYA levels pretty high, then I lose much if not all my chlorine over the course of the day. That's why you'll find posts of mine that refer to my ideal CYA, which is 80-90 ppm FOR MY POOL. (I would never recommend it that high for pools without similar circumstances to mine). So...although it's hard to say how much chlorine you're using up daily because I don't know what the peak was to begin with, if you think you're losing too much, you might try to "up" the CYA level JUST A LITTLE and see if that helps.

One reason that you'll find your chlorine levels fluctuate instead of staying steady like they did with the chlorinator, is that the chlorinator added a steady stream of chlorine as long as the pump was on....with bleach or cal-hypo, you need to add it as late in the evening as you can (after the sun is off the pool), to get as much sanitizing time out of the chlorine as possible--and make sure you put enough in to leave a residual by the next night.

Janet

[Water_man]

The FC in the chart is the level before the treatment.
I haven't measured the FC immediately after the treatment because it takes time for the water to circulate and to evenly distribute the added FC.

[aylad]

I haven't measured the FC immediately after the treatment because it takes time for the water to circulate and to evenly distribute the added FC.

Yeah, I get that.. But my point was that there's no way to determine how much chlorine loss you have without knowing the peak to begin with. You can get a good idea of the peak, assuming no algae problems, by adding your chlorine in the evening and then measuring early in the day before the sun hits the pool. Or add it, let it circulate for a couple of hours, then test....it'll give you at least a ballpark.

Janet

[Water_man]

Yeah, I get that.. But my point was that there's no way to determine how much chlorine loss you have without knowing the peak to begin with. You can get a good idea of the peak, assuming no algae problems, by adding your chlorine in the evening and then measuring early in the day before the sun hits the pool. Or add it, let it circulate for a couple of hours, then test....it'll give you at least a ballpark.

Janet

OK. Already got yesterday's late PM reading. Added chlorine last night (shooting for FC 6.8 as per chem geek's chart) and measured this moring (pump worked non-stop.) Will measure again at eve and will post all numbers. Thanks

[Water_man]

OK. Already got yesterday's late PM reading. Added chlorine last night (shooting for FC 6.8 as per chem geek's chart) and measured this moring (pump worked non-stop.) Will measure again at eve and will post all numbers. Thanks

Alright, Janet, I have the numbers.
On Thursday, 5/29 at 4:30 pm I had FC 4.5.
I added chlorine at night time an amount calculated to reach 6.8.
After all night of ciruclation, today's 8 AM reading was 6. Today's 7 PM reading was 4.5.
Again, CC has always been <0.5 , although non-zero.
Does it make sense that with CYA 60 I lose 1.5 ppm a day for UV degradation?
Is it possible that FC is consumed by the polyquat?

[Watermom]

Does it make sense that with CYA 60 I lose 1.5 ppm a day for UV degradation?

Yes, even with cya in your pool, you will still lose chlorine especially on hot, sunny days.

[aylad]

Yes, it makes sense...in fact, I'm surprised it's not a little higher than that. If you want to try to reduce the loss, you could try to up your CYA just a little and see if it makes a difference, but honestly 1.5 ppm daily isn't a bad number at all.

Janet

[Water_man]

Yes, it makes sense...in fact, I'm surprised it's not a little higher than that. If you want to try to reduce the loss, you could try to up your CYA just a little and see if it makes a difference, but honestly 1.5 ppm daily isn't a bad number at all.

Janet

Thank you aylad and watermom for your responses.
I've been adding bleach on a daily basis now, in order to maintain the 4-6.8 ppm FC as per the table (CYA=60.)
Since it is recommended to add chlorine at night, does it make sense to keep the pump working 24/7?
I wonder what everybody else is doing.

[aylad]

I only run my pump 9-12 hours a day during swimming season (turn it on when I get up, off when I go to bed, except when the water gets too hot, then I do it opposite). My pump time decreases to a couple hours a day during the winter.

If you're not using a SWG or trying to clear up an algae bloom, I don't think 24/7 is necessary.

Janet