Net chlorine loss

[P3Jason]

Let me know if my logic is sound on this. I did a full set of tests on Tuesday, 16 May, in the evening. Results:

FC 7ppm
CC 0 ppm
pH 7.4
TA 120 ppm
CYA 55 ppm
CH 180 ppm
Temp 83 deg F

I added 32 oz of liquid chlorine immediately after testing and checked again almost an hour later and got 8 ppm FC. I tested FC again the next day, mid afternoon and got 5.5 ppm. 64 oz of chlorine went in. Tested again that evening with a result of 6.5 ppm. I figure that my normal loss rate is 3.5 ppm FC per day, on a typical sunny Florida day with no bather load. Historically, 32 oz of chlorine will give me 1 ppm FC, so to maintain FC in the butter zone I'll need to add just under a gallon of chlorine per day, more when the pool has been used or after heavy rainfall. I'll still test at least daily until I can derive a pattern. I'd just like a sanity check.

 

[Richard320]

3.5 ppm per day sounds a little high for no bather load.

I'd suggest an Overnight Chlorine Loss Test to be sure there's no algae growing somewhere. You can do it over the weekend. Boost FC up and let it mix and test FC after the sun goes down. Leave the pump run all night. Set the alarm and get up and test the FC before the sun hits it. Then you can go back to bed if you want.

Two things consume FC: sunlight and organics. You just eliminated sunlight, so if you didn't lose any, there's no organics and you're good. If you did lose more than 1 FC, something is growing in the water. Kill it.

 

[P3Jason]

Last evening I vacuumed, brushed, and cleaned the filter. I dosed with chlorine and later tested at 9 ppm at 8:30 pm. Testing at 6:50 this morning, FC had only dropped to 8.5, pump having run all night.

 

[duraleigh]

Your logic and math all make sense. 3.5 daily FC loss is probably a little high. I think you'll find your loss will be closer to 2 ppm.

You could simply dose for that by adding 2 ppm daily and see if your FC goes up, goes down or remains steady.

 

[Richard320]

Last evening I vacuumed, brushed, and cleaned the filter. I dosed with chlorine and later tested at 9 ppm at 8:30 pm. Testing at 6:50 this morning, FC had only dropped to 8.5, pump having run all night.

Well, that pretty much rules out algae. Is there any chance that chlorine of yours is leftovers from last year? That would make it weaker and so you'd use more.

 

[P3Jason]

Well, that pretty much rules out algae. Is there any chance that chlorine of yours is leftovers from last year? That would make it weaker and so you'd use more.

Chlorine is fresh. I just bought 4 jugs earlier in the week. I dosed to a little higher level last night in an effort to not flirt with minimum FC so I can test this evening and see what the gross 24 hour loss is without having to dose in between.

 

[lmnconn]

Even though you just bought the chlorine, it might be leftover from last year's stock at the store. I seem to run into problems every year since I open my pool in April. By mid May the issues resolve and I'm assuming it's because they have sold all the old chorine and finally have fresh.

I will have a 3-4 part loss, per day when I first open the pool, but by May I'm only losing 1.5. (at the same CYA level)