Questions about .5 CC and FC usage

[nnichols]

I've just converted to BBB on my 18,600 gallon AG pool. I've fought this beast for two years, and I think I've finally got it whipped. I killed a heavy algae bloom last week, and I've lowered my CYA to 45 by replacing 1/2 of the water.

I started with my TF100 kit on Friday, and I've ran tests two nights in a row. Currently the pool is clear and looks good.

Friday night, I was at 8 FC, .5 CC, at 45 CYA. Tonight I came up with 4.5 FC, .5 CC. It was fairly hot today (temp around 98, water temp @ 85). I hit it with 19oz of 6% bleach after testing tonight, to get to 5, per the recommendations of the Pool Calculator.

So at this point I have two questions:
1. Should I shock based upon the .5 CC reading? Would my FC usage slow down if I got rid of this .5 CC?
2. What would be considered a normal amount for FC to drop daily assuming no issues with water quality?

Thanks!
Nathan

 

[frustratedpoolmom]

.5 CC is minimal, not worth shocking, especially if your water is clear. Now if it was cloudy or greenish or something and you had that test result, of course I'd say shock.

That chlorine loss is fine. It's about a 2ppm a day, normal usage. Many people even with your CYA level report a 50% chlorine loss during the day, especially if they don't use a solar cover, live in hot sunny climates, etc.

Just remember to test your FC and PH every day or every other day and make adjustments as needed. Never let your FC drop below your minimum target and you should be fine.

 

[JasonLion]

Welcome to TFP!

No need to worry about CC at 0.5. You only need to shock if it gets higher than 0.5.

With CYA around 45 you should expect to lose on the order of 50% of your FC each day, plus or minus depending on how much direct sunlight you get. You always want to keep FC at 3 or higher, so raise it to 6 in the evening and lose 50% would mean about 3 ppm a day.

 

[AnnaK]

Hi Nathan,

Welcome to TFP.

My CYA level is at 40 ppm. I keep the FC between 5 and 6 ppm and lose between 1 and 2 ppm in a 24 hr period. It depends a lot on how much swimming we've done. If nobody has been in the pool the loss is 1 ppm. Our pool is in full sun.

I test pH, FC, and CC daily, usually around 10:00 a.m. Sometimes I get a .5 CC reading, sometimes not. I've not been able to correlate that to anything at all: not swimmer load or activity, not weather (rains), not dust in the air or dirt on the pool bottom. Since my water is very clear and the pH runs at a steady 7.5, and since I can't see any algae when I do a snorkle inspection, I just don't give that .5 CC another thought.

The last time I shocked the pool was in late April when we opened it.

 

[nnichols]

Thanks all for the replies. I'm thrilled that I've been able to keep this pool stable for over a week straight now. Originally it had a DuoClear/Nature2 system on it (came with the house when we bought it) and it was a constant battle. The control board burnt out in the spring, so I decided to go straight chlorine. I officially unwired and removed the control box yesterday, and plan on removing the inline section soon.

I now understand the relationship between CYA and required FC levels. However, if I were to run a higher CYA and associated FC levels, would that change the amount of added chlorine daily to maintain? For example, if I ran a 75 CYA, and ran higher FC at 6-11, would the FC hold longer, hence requiring less added chlorine each day?

Thanks!

 

[JasonLion]

Right, raising the CYA level means less total chlorine used.

 

[nnichols]

Thanks, I am going to run more of my trichlor until I hit around 60 CYA.

 

[AnnaK]

FWIW, I'm one of the few people here who uses a trichlor feeder throughout the swim season.

My pool freezes solid during the winter and starts out with 0 CYA. I add enough granular CYA to raise it to 20 ppm, then use the feeder at a relatively low setting: 1/8 of fully open. We begin to run the pump (and the feeder) at the end of April and I'm now at 40 ppm. I expect to close at the end of October with somewhere around 60 ppm of CYA.

You can see from my earlier post in this thread that I have only a small actual FC loss in any given 24 hr period because chlorine is being added via the trichlor pucks. My pump runs 8 hrs each night. I add approximately 2 cups of liquid chlorine (estimated effective concentration of 10%) every 3rd day or when the FC reads 5 ppm.

For me, the combination of a trickle of trichlor in combination with small additions of chlorine has proven to be very cost effective and efficient. The CYA rise is so slow that it has never reached above 60 by my own weekly tests and those done monthly by the pool store. I don't know what happens to the CYA over winter. The pool is not covered. Maybe it's broken down by freezing and sun exposure. This system works well for me though it may not work for everybody. Each pool is different.