Not new to this... Where is my FC going?!


Well-known member
Jun 4, 2014
Shrewsbury, PA
Hi everyone,

I've been using the TFP method for about 4 or 5 years now and have not had an issue since converting. But now, I have a FC loss mystery and I suddenly feel like I have no idea what I'm doing.

Going to give a little back story in case it somehow plays a part...

About a month ago I started having an issue with Grackles - those birds that deposit their babies' poo into swimming pools. It was the first time I had experienced CC in a couple YEARS! I cleaned out the mess, did a SLAM, and managed the Grackle poop by using fake snakes and pool floats to deter them, and kept the solar cover on to keep poop out. Each day I would have one or less poops that made it into the pool.

During this time, occasionally there was a negligible amount of CC... and by negligible I mean I couldn't tell if the sample actually turned slightly pink or I was imagining it, or it was reflecting off my pink shirt, etc.

The Grackle babies have since moved out and there has been zero sighting of a Grackle poop in about a week now.

Onto the present issue... the massive amounts of FC I'm losing. I noticed the large amount of FC loss during the Grackle event, but I attributed it to actual chlorine loss due to their being bacteria in the pool from the Grackles. Again, occasionally I MIGHT be seeing some CC, but I also might be willing it to exist. The FC chlorine loss I'm talking is about 8 EIGHT ppm per day.

Last night I raised to shock level, moved the steps, brushed, vacuumed, emptied skimmer, emptied pump basket, did the whole nine yards as far as cleaning.

Last night's readings when I started this SLAM were

FC 12
CC 0
TA 70
pH 7.3
CYA 30 (yes 30... but I'm suspect of this as I will mention soon)
CH (vinyl liner and don't care) 100

I then cleaned the pool and ran to the store to stock up on ALL the bleach. Came back, about 1.5 hours later,

FC 10.5
CC 0 (or maybe a trace or my imagination)

Raised FC to 13.5 (a little over slam level but I knew I'd lose a lot over night... or so I thought)

This morning 7:15 am (sun had been up for a little over 1.5 hours)

FC 11.5
CC 0

So 2ppm FC loss overnight (which I know fails the overnight chlorine loss test) but the sun had already been up for a little bit.

I left it alone at 11.5, just checked at 10:15, so 3 hours later

FC 8
CC 0

3ppm FC loss in 3 hours! Full sun.

I did another CYA check because I just can't comprehend the sparkling clear water and 0CC and still get a reading of 30.

Is something really lurking in my pool? Or do I just need to raise my CYA to maybe 50 due to full sun (morning noon and evening)? Every other year I've had my CYA in the 30-50 range and been fine.

Also, something else I want to add in case it helps solve the mystery...

When I add the DPD powder, the sample turns pink like usual. When I start the drops to check for FC (names are escaping me) the sample gets a bit cloudy. When I add the other drops (again I forget) to check for CC, it gets even more cloudy. Only thing I could find online is too high calcium hardness but as you will see from above, that's not the case.

Any help would be greatly appreciated... by both myself, my back account, and any other Walmart shoppers that would also like to buy some bleach but can't :)

P.s. Happy 4th!
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Reactions: kateinvt


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Add 10 ppm of CYA. That should help the daytime FC loss.

The FAS-DPD test sample does get cloudy. Only think you care about is the color. Once the pink/red is gone, it is done.
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Reactions: LaurenB


Well-known member
Jun 4, 2014
Shrewsbury, PA
Once you pass the SLAM criteria, add the CYA.
Ah, crud! I already tossed a sock of cya in the filter then headed out for a few hours before seeing this.

Interestingly though at 12:15pm my FC was 8. Tossed in the sock of cya. Just now at 4:15pm I checked and it is at 7. Can CYA start to work that fast? CC still 0... or maybe just the slightest tinge of pink I really can’t tell.

To recap, I lost 3ppm in 3 hours earlier today. Added 1lb 5oz cya at 12:15 and 4 hours later only lost 1ppm.

Also, it did get cloudy and we’ve had a thunderstorm/rain since about 1:30.

Do I assume I now have 40 CYA and to raise my FC to shock level according to that?

Thanks so much!


Well-known member
Jun 4, 2014
Shrewsbury, PA
Last night I did a correct OCLT and I lost 1.5 ppm ... D’oh! So close.

Can my solar cover be on overnight while checking for an OCLT? My water level is getting low due to no rain and I have very hard well water so I try to avoid topping off as much as possible.

Thanks again!