FC dropping

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
So, thanks to this forum and the TFP pool test kit, I have been taking care of my pool for the past two years after having my pool built. Things have been going pretty good overall, but prior to going on vacation, I must have accidentally added a bit too much stabilizer; I normally keep the CYA at 50-60 and its up at about 80. I didn't think that was a big deal, but now I cannot get and keep my FC levels above 1ppm.

The kids have been using the pool a bunch, so I thought maybe that was the 'problem'. About 4 nights ago, I ran a boost on the SWG at 90% for 10hrs. It got the FC level to 2ppm, but within a few days its back down to 0.5ppm. I normally run the SWG 70% in the summer but due to the FC levels, I bumped it up to 85% and added a couple hours. Still no change.

I thought maybe the SWG was going bad, so I took it out for a quick check and everything looks really good, and there are no error messages or anything on the display (pool builder said this would happen if it went bad). Still, I put a hose on the return closest to the pump and filled my sample cup. With the SWG operating at 85%, I was only getting 1ppm of FC in the water coming out of the return. Of course the builder mentioned checking phosphates and from what little I have read here, that seems like a waste of time.

I'm thinking my elevated CYA level is the issue but want to get some expert advice. Last log values from yesterday are below.

FC - 0.5ppm
CC - 0.5ppm
pH - 7.4
TA - 70
CH - 325
CYA - 80
TEMP - 91
SALT - 3700
CSI -0.38
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,524
Laughlin, NV
Do a Overnight Chlorine Loss Test

How does the water look?

Can you post what Brand/Model SWCG you have? The information in your signature does not lead to any data.

Add 1 1/2 gallons of 10% liquid chlorine now. Use it to raise your FC to 10 ppm tonight for the OCLT.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Do a Overnight Chlorine Loss Test

How does the water look?

Can you post what Brand/Model SWCG you have? The information in your signature does not lead to any data.

Add 1 1/2 gallons of 10% liquid chlorine now. Use it to raise your FC to 10 ppm tonight for the OCLT.
I'm so sorry....realized I put the serial number in for my SWG. It is a PLC1400. I'll change here in a few.

The water looks great.....clear, no signs of cloudiness or algae.

I'll do the drop test tonight per your recommendations and post results.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,524
Laughlin, NV
Your standard SWCG run time of 10 hours at 70% creates 2.6 ppm FC in your pool. That would be on the low side for Florida in summer. I would target at least 4 ppm creation once you get this ironed out. For 10 hours running time, you would need to set the generation at 100%.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Your standard SWCG run time of 10 hours at 70% creates 2.6 ppm FC in your pool. That would be on the low side for Florida in summer. I would target at least 4 ppm creation once you get this ironed out. For 10 hours running time, you would need to set the generation at 100%.
Thanks Marty.......
Also worth a note, I do have a screen enclosure. I always assumed (by the lack of sunburns) that this blocked some UV. Not sure if it applies, but assumed it might reduce the FC breakdown some.

If I may ask, how did you calculate that? Also, is there any component to the calculation that is related to pump flow?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,524
Laughlin, NV
Add the screen enclosure to your signature -- it will reduce UV impact.
Use PoolMath. Effects of Adding Chemicals.
Flow rate does not impact chlorine generation by a SWCG as long as your flow rate is high enough to close the flow switch on the SWCG.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Add the screen enclosure to your signature -- it will reduce UV impact.
Use PoolMath. Effects of Adding Chemicals.
Flow rate does not impact chlorine generation by a SWCG as long as your flow rate is high enough to close the flow switch on the SWCG.
Wow Marty.....that is so cool. Really appreciate the help there! That is a really nice feature and I had zero idea about it. Its really nice that all those SWG's are listed. Kudos.

BTW, I added the CL and will perform the drop test tonight. I'm thinking though, based on all info to date, the SWG just isn't producing enough given the summer conditions. Weird that it was ok the previous two summers but.......hard to say at this point.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
OK..... FC at 10ppm last night and down to 7.5ppm this am. So something is consuming FC. Guess I will do my first SLAM; I'll prepare today and start tonight/tomorrow.

I have read the SLAM instructions and seems pretty straightforward. CYA at 80 means I need to bring the FC up to 31ppm. I just ordered replacement powder and R-0871 a few weeks ago, so should be good testing-wise. I'll pick up some CL at Pinch-A-Penny later today (figuring qty.3 of the 2.5gal CL).

As mentioned in my signature, I have a spa. The design of the pool, which seems pretty standard, is that the spa is one of the returns and there is a spill over into the pool. I would imagine during the brushing every day I need to hit the spill over area since it doesn't flow into the pool but kind of trickles down some rough cut tile.

Couple other questions:
1. Do I perform the OCLT every night? My water is clear, so not sure if I should begin OCLT right away or wait a few days.
2. I turn the SWG off, but do I need to operate the filter pump 24hrs/day while SLAMing?
3. Brushing/vacuuming - does it matter when or in which order you do these?

Thanks all!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,524
Laughlin, NV
1. No reason to do a Overnight Chlorine Loss Test until the water is crystal clear, no visible algae or debris.
2. Leave the SWCG off. Pump should be run continuously .
3. Some say vacuum first so you can pick up debris before the brushing pushes it into the water column.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Small update......
Starting on day 3. I've been through qty.5 of the 2.5gal jugs of CL. I noticed something last night and was hoping for some guidance.......

I performed the FC test and got a level of 36ppm. Thought it was high for the amount of CL I had added so tested it again. Next time it was 31ppm. Tested a third time and it was 32ppm. All using the same water sample. Now I had been running my 871 drops in 'faster' during the SLAM just due to the amount of drops required; does the rate at which you form and release the 871 droplet affect it's size at all and therefore slightly affect the perceived FC level?

Both the 870/871 were just recently purchased. I did try to conserve the 870 a bit by lowering the 'heaping helping' to just a helping. I'm Just trying to figure out why there would be a discrepancy, especially when I have to perform the overnight FC drop test.
 

CrystalRiver

Well-known member
Jun 19, 2020
234
Massachusetts
Yes, drop size is impacted by how fast you drop it in. That's why the instructions say to add drops at about 1 per second, letting each drop cling to the tip before falling under its own gravity. It is also important that the dropper is held straight up and down, for the same reason. Drop size.

There is also error in any test. Even with perfect technique, that test is limited to plus or minus 10% accuracy. At 70 drops, that's plus or minus 7 drops.
 
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Mike1162

Silver Supporter
Jun 13, 2015
719
N Tonawanda, NY
After adding the 870 powder & swirling you want to see some powder that doesn't dissolve. Even one undissolved grain of powder means you put in enough. The speed at which you preform the test can effect the results. I imagine the drop size could be effected by trying to do it faster, try to let the drop form & let gravity do its thing.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Yes, drop size is impacted by how fast you drop it in. That's why the instructions say to add drops at about 1 per second, letting each drop cling to the tip before falling under its own gravity. It is also important that the dropper is held straight up and down, for the same reason. Drop size.

There is also error in any test. Even with perfect technique, that test is limited to plus or minus 10% accuracy. At 70 drops, that's plus or minus 7 drops.
Makes sense....thanks for the clarification. So when doing the OCLT, do I take an average of 3 tests per water sample? Plus or minus 7 drops is plus or minus 3.5ppm of FC. Not sure how that would work if I'm shooting for max 1ppm of loss.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
After adding the 870 powder & swirling you want to see some powder that doesn't dissolve. Even one undissolved grain of powder means you put in enough. The speed at which you preform the test can effect the results. I imagine the drop size could be effected by trying to do it faster, try to let the drop form & let gravity do its thing.
Thank you as well. I'm using the Taylor stirrer, so as long as I hear the extra scratching in the bottom, I will assume I'm good to go.
 

CrystalRiver

Well-known member
Jun 19, 2020
234
Massachusetts
Control for what you can control for (pump running >30 minutes before collected ng sample, collecting sample from the same location, test technique) and don't worry about the rest. Just test once in the evening and once in the morning for OCLT. If your FC "rises" or is within margin of error, call it good. Pass two OCLTs in a row, plus meeting the other criteria, then let your FC drift down. You can keep doing OCLTs as it comes down if you'd like.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Control for what you can control for (pump running >30 minutes before collected ng sample, collecting sample from the same location, test technique) and don't worry about the rest. Just test once in the evening and once in the morning for OCLT. If your FC "rises" or is within margin of error, call it good. Pass two OCLTs in a row, plus meeting the other criteria, then let your FC drift down. You can keep doing OCLTs as it comes down if you'd like.
Thanks again. I have been doing everything pretty consistently. The pump has been running 24/7. I take the sample from the same location and depth. My 871 additions have been the only 'variable' and I honestly never would have thought about it until my 'issue' last night. I will try to have more control in the 871 additions today and see what happens. I'll do my first OCLT tonight and post results here for best guidance. Fingers crossed.
 

Thegatorvault

Active member
Jun 10, 2018
41
Tampa FL
Starting day 4.......
Did my first OCLT last night. Results below:

9:30p - 34ppm
8:20a - 24.5ppm

A couple things to mention, and not sure it would have an effect or not:
1. The day yesterday was pretty overcast, but we had some showers in the afternoon. I noticed at about 6p that there were a bunch of little black bugs that had gotten washed into the pool. My guess is they were gnats that were on the enclosure and fell victim to mother nature's wrath.
2. We had friends over for dinner last night (no swimming) and enjoyed some wine i.e. I did not make my 7am wake up for testing target. At 8:20, there was just a bit of direct sunlight on the pool.
3. Pool consumed 2gal of CL yesterday to maintain target (additions every 2-4hrs).

Plan is to forge ahead and maintain levels today with another OCLT tonight. Water has been crystal clear since day 2 with no visible signs of algae anywhere (that has been constant).

Any thoughts?