High FC and TC for 2 weeks

[tkan86]

Hi there everyone!
I'm a new home/pool owner and new to the thread - have been lurking around and not sure if I'm seeing anything specific to my problem so here goes... (I apologize, this is extremely long)

----Backstory----
We moved into our home a little over 4 weeks ago and the pool has been nothing but frustrating. The previous home owners had a pool inspection, which showed high CYA (in the 100's), no FC/TC, and high phos (in the 2000-3000's if I remember correctly). The water was minimally cloudy per the report but otherwise no other major findings. The previous home owners drain the pool 1/3 every year (not exactly sure what their reason is for this - maybe persistently high CYA?) and use chlorine tablets for maintenance, Shock as needed. Also, there are trees everywhere, and in pretty close proximity to the pool.

1.5 weeks after moving in, we had a pool company come out to do another inspection and for weekly maintenance since we knew nothing about owning let along maintaining a pool. Similar findings as above. A few days later, the pool turned green and our sweeper (old barracuda that came with the house) stopped functioning. The pool guys shocked the pool and replaced the barracuda with a G3 that's also not functioning - the pool is now dark green and cloudy with no sweeper. The goes on for about 1.5 weeks (they came and replaced a bunch of valves to try and trouble shoot the sweeper but couldn't figure out why it wasn't working, then tells us the sweeper is not important) so I take a sample of the water and go to Leslie's (7/24/22):
FC: 0.1ppm
TC: 0.1
pH: 7.5
TA: 131 ppm
CYA 166 ppm
Phos: 5757 ppb
TDS: 3300 ppm

I bought some supplies to shock the pool myself (power powder plus). The pool is lighter green but still cloudy. Brought a sample to Leslies (7/26/22):
FC 4.9ppm
TC: 6.01
pH 7.8
CYA 134
Copper: 0.7ppm
Phos: 6352 ppb
TDS: 3400 ppm

The pool guys come back one more time and shock the pool again and this turns the pool (3 days later) blue but it's so cloudy you couldn't see the sweeper at the bottom of the pool. They came back to clean the filter again to see if this helps (2nd filter clean in 2 weeks). The pool is looking better, but I'm noticing the FC levels creeping up (7/30/02). Also, during these periods, I have been replenishing my pool with new water.
FC: 20.51 ppm
TC: 20.51
pH: 8.1
TA: 92
CYA: 129
Copper: 0.3ppm
Phos: 4906
TDS: 2450

The pool guys wouldn't answer my questions about why the sweeper is not working so I go on to youtube and learn how to take the barracuda apart - the diaphragm was torn and clogged so i replaced it. Pool guys charge me for the barracuda at this point, and now they are fired. I added muriatic acid to bring the pH down and next day (8/2/22):
FC: 25.25
TC: 25.25
pH: 7.9
CYA: 149
Copper 0.4
Phos 4000 (out of range on their machine - but i think it was in the 6000's)
TDS: 2400

----Current problems----
The pool is now super clear but here is where I'm having issues:
- I have not added any source of chlorine (tablets, liquids, etc) since the pool was shocked by the pool guys a little over 2 weeks ago and my chlorine is still super high - it maxes out on Leslie's machine around 25ppm so I don't know if it's started off super high and is coming down slowly, if it's not changing, or if it's going up. We've been having pretty hot days in Northern California (90's) and my pool gets direct sunlight 4-5 hours out of the day. Because I'm paranoid, I used a test strip on the water that I'm filling the pool with and confirmed there's no chlorine being added. I checked the skimmer filter and cleared the debris but no tablets I could find. I bought the Taylor 2006c kit, filled to 25 ml, and had 140 drops of the reagent and the water was still light pink - I gave up at this point (at least 28ppm FC).

- CYA obviously is still high - I have a fiberglass pool. Any recommendations? I've been doing very small draining of the pool (1-2 inches at a time, fill up and let the filter run; drain another 1-2 inches the next day, fill up, etc). Is the high chlorine because of my high CYA?

- Phos is still high - I did a noPhos treatment (yea, i know, should have gone with the PR 10000) and that didn't budge the phos.

- Lastly - the last week, I noticed very well defined marks on the floor of the pool. They are dark (I think brown color) spots with clean edges, and I can't get them off with the nylon brush I have no matter how hard I scrub. They are scattered at the bottom below where the skimmer is, and where the jets are. They don't seem to be getting worse. On 8/3/22, I found one of those Pool RX baskets with Copper that the pool guys placed in my skimmer - could this be the cause of the marks? I'm unable to reach the marks to test with chlorine vs. Vit C without completely submerging myself in a pool with an unreadable chlorine level.

Last reading by Leslie's (8/5/22):
FC: 25
TC: 25
pH: 7.9
TA: 129
CYA: 144
Copper: 0.3
Phos: 5000's
TDS: 3400

Sorry for the long story, but it's been a long road - I still haven't been able to use the pool since moving in. Any advice/similar stories would be much appreciated!

 

[Texas Splash]

Welcome to TFP! I can sum-up your situation with 3 words - proper test kit. Or I could also say "Avoid pool store".. You really need to test your water with your own TF-100 (link in my signature) or Taylor K-2006C test kit. Everything you do (or we advise) starts there. You cannot trust those numbers above. Store testing is often flawed and throws off your actions.

Also be sure to bookmark our Pool Care Basics page for tons of great info.

 

[DrewLG]

Welcome. It's great that you have a K-2006 kit. Stop going to Leslie's (except for that copper test, maybe) and trust your own kit exclusively. To cut down on your reagent consumption, use a 10ml water sample for the chlorine tests instead of 25ml (and correspondingly use one heaping dipper of powder, and only 5 drops of R-0003 for the CC test). With a 10ml sample, each drop of R-0871 indicates 0.5ppm, which is fine; you don't need 0.2ppm resolution for a pool.

Your high chlorine readings might not be from chlorine at all. Do you know whether the pool guys used a ton of non-chlorine shock (potassium monopersulfate, aka potassium peroxymonosulfate or MPS or KMPS) to clear your pool? That chemical will interfere with chlorine tests and doesn't burn off as quickly as chlorine. If you want to know for sure, Taylor sells a deox reagent kit that kills the interference so you can measure FC and CC separately from KMPS.

Expect to drain and replace at least half your water (probably more, if the Leslie's test is accurate -- do your own test to confirm) to lower your CYA concentration to something reasonable. No, high CYA isn't what's making your FC read so high.

Expect to perform a SLAM to clear the algae. Read up on the process in the Pool School section of the site. If you want, you can remove the phosphates before the SLAM (Seaklear Phosphate Remover works way better than what you tried, and is priced accordingly). That might make the SLAM go a little faster, but it isn't really necessary. Once your pool is crystal-clear after the SLAM, you can ignore phosphate levels if you continue to follow the TFP maintenance methodology -- because although phosphates are algae food, there won't be any algae in your pool.

The stains could well be because of copper in the water. Remove the PoolRx product, then read the Metals section in the TFP wiki. Optionally, also call up the pool guys you rightly fired and curse at them.

 

[tkan86]

Thank you both for your replies! I went back through my receipts and it looks like they used 12 gallons of liquid chlorine during the last time they shocked the pool (the first time they used 2.5 gallons) - maybe that's why it took forever to come down? I'm in the process of doing a slow drain/fill of my pool because I redid the k-2006c kit and got the following results (this was performed 2 hours following a 1 inch drain/fill of my pool today)

FC: 13.5 ppm (finally got an actual number)
CC: 0.5 ppm
pH: 7.6
CYA: 340 (after a 3:1 dilution) ppm
TA: 200 ppm
CH: 322 ppm

At least the pool looks clear

Based off of this, I'm assuming continuing to drain/refill pool, retest, maintain the chlorine? Also, from my searches/reading, it looks like using liquid chlorine/bleach is everyone's to-go method for maintaining their chlorine levels and it's done on an as needed bases depending on how low the FC drops?

Thank you!

 

[DrewLG]

[Oops, duplicate post.]

 

[DrewLG]

it looks like they used 12 gallons of liquid chlorine during the last time they shocked the pool

For a 17000 gallon pool, that would have raised your FC level to almost 90. Which actually IS the appropriate shock level for your 340ppm CYA, so maybe they accidentally did something almost right.

I'm assuming continuing to drain/refill pool, retest, maintain the chlorine?

Assuming that your CYA measurement is correct, you'll need to do around 120 of those 1-inch exchanges to lower CYA to 60ppm. And you'll end up replacing nearly twice the total volume of your pool. (Back-of-envelope estimate, assuming 1 inch is 250 gallons for your 17000 gallon pool.)

If you can do 12 inches at a time, you'll get the CYA down to 60 in only 9 exchanges, although that means you'll be dumping 3000 gallons at a time, which may be significantly more trouble than 250. And you'll still end up replacing 27000 gallons.

Also, from my searches/reading, it looks like using liquid chlorine/bleach is everyone's to-go method for maintaining their chlorine levels and it's done on an as needed bases depending on how low the FC drops?

There's more to it. The TFP method starts with (buying a good test kit and then) eliminating all algae by raising the FC level to 40% of CYA concentration, and continuously maintaining that level while brushing and cleaning until the algae is gone (i.e., until free chlorine is no longer being lost to algae). Your high CYA makes this step impossible. After the algae is gone, the method is then to maintain FC at around 10% of CYA concentration to ensure that there's always enough HOCl in the water to keep it sanitized and algae-free. Even if your pool were already algae-free, your high CYA would make this ongoing maintenance very difficult.

But yeah, once you get your CYA down, liquid chlorine (or an SWCG) is the only reasonable way to chlorinate your water -- because the solid forms of chlorine contain either CYA or calcium, both of which are undesirable at high levels, and both of which will accumulate and remain in the pool water more-or-less forever, or until the water is drained.

 

[mgtfp]

I went back through my receipts and it looks like they used 12 gallons of liquid chlorine during the last time they shocked the pool (the first time they used 2.5 gallons) - maybe that's why it took forever to come down?

Yep, that would explain it. Your FC would have be much higher after those 12 gal as DrewLG already calculated. I guess that the pool store test maxes out at some point and you never saw the real FC in their test results. And together with the CYA of 340 it took a while to come down

Lastly - the last week, I noticed very well defined marks on the floor of the pool. They are dark (I think brown color) spots with clean edges, and I can't get them off with the nylon brush I have no matter how hard I scrub. They are scattered at the bottom below where the skimmer is, and where the jets are. They don't seem to be getting worse.

They likely are metal stains as you were already suspecting. After the addition of 12 gallons of chlorine, pH would have been through the roof, which has likely brought dissolved metals out of solution.

Even though chlorination with bleach is pH-neutral regarding to whole chlorination cycle, there is one aspect to consider: Adding liquid chlorine raises pH. The following "use" of chlorine (i.e. chlorine killing nasties and oxidising things, and chlorine decay by UV-light) is an acidic process that compensates the initial pH rise. By the time FC is back to the level it was before the liquid chlorine addition, pH is back down to where it was before.

In normal pool mode with regular small chlorine additions to maintain target FC levels, those pH fluctuations are small enough to be ignored.

But adding large quantities of chlorine and then maintaining the increased FC will come with a significant rise in pH. That's why it's important to reduce pH before starting a SLAM.

Adding 12 gallons of liquid chlorine all at once sounds out of control to me.