Lowering combined chlorines

[SR71P52]

Hey all!

I have a 29k gallon in-ground plaster pool and been trying the TFP method this season and have a tf-100 test. So far I have had my free chlorine levels dissipate very quickly despite having a CYA around 40. My combined chlorine is continuously rising throughout the season and is currently at 8ppm. The water is clear and beautiful. I have tried shocking the pool many times with bleach, raising the FC to 14 according to pool maths recommendations, but have not had luck lowering my combined chlorine.

FC: 4
CC: 8
PH: 7.6
TA: 160
CH: 500
CYA: 40

I also have some confusion about the fas-dpd test. I notice that when adding the drops the pink liquid will turn clear at some point but within 15 seconds or so turn a light shade of pink again. It continues to do this after many drops. At what point is the titration complete?

 

[Msch99]

Is your pool covered a lot? When mine is on for extended periods the cc accumulate. From what I understand the UV rays burn it off.
Ignore turning pink after it is clear the first time.

 

[Richard320]

The first time the test goes clear is the reading you want. If you leave it sit, oxygen in the air will react and turn it pink again.

I really wonder if CC is 8. It would reek like a health club hot tub -- that burn-your-eyes chlorine smell.

 

[SR71P52]

The first time the test goes clear is the reading you want. If you leave it sit, oxygen in the air will react and turn it pink again.

I really wonder if CC is 8. It would reek like a health club hot tub -- that burn-your-eyes chlorine smell.

The pool hasn’t been covered since it was opened in early May. I have been doing the test like that, stopping drops as soon as it turns clear. After adding the dpd powder, the sample only runs very light pink. Once I add the combined chlorine reagent drops, the sample turns very dark pink. I don’t smell anything very heavily of chlorine in the pool however...

 

[Richard320]

The pool hasn’t been covered since it was opened in early May. I have been doing the test like that, stopping drops as soon as it turns clear. After adding the dpd powder, the sample only runs very light pink. Once I add the combined chlorine reagent drops, the sample turns very dark pink. I don’t smell anything very heavily of chlorine in the pool however...

Next question: has anyone added any non-chlorine shock to the pool? Like Leslie's Fresh N Clear or Renew or Oxybrite? Because those can misread as CC.

 

[SR71P52]

Next question: has anyone added any non-chlorine shock to the pool? Like Leslie's Fresh N Clear or Renew or Oxybrite? Because those can misread as CC.

Nope, only thing added in the pool has been dichlor shock and trichlor tabs early in the season(until CYA was high enough). Last few weeks have been pure chlorine bleach only.

 

[Richard320]

Nope, only thing added in the pool has been dichlor shock and trichlor tabs early in the season(until CYA was high enough). Last few weeks have been pure chlorine bleach only.

Then all I can say is that you have something growing in there. Shocking to 14 once isn't a SLAM. It needs to get up to 16 FC every few hours for a few days until all that CC is eradicated and you pass the overnight loss test. SLAM Process

 

[SR71P52]

Then all I can say is that you have something growing in there. Shocking to 14 once isn't a SLAM. It needs to get up to 16 FC every few hours for a few days until all that CC is eradicated and you pass the overnight loss test. SLAM Process

I will try this process until I meet the SLAM guidelines. Also I opened my filter and noticed some blue substance that I’ve never seen before... any idea what this could be? Maybe this is why the CC is so high.

 

[mknauss]

Copper. Have you used copper algaecides, copper containing shock or tablets, in the past? Do you have a heater?

 

[SR71P52]

Copper. Have you used copper algaecides, copper containing shock or tablets, in the past? Do you have a heater?

I used some dichlor shock which had copper very sparingly about a month ago. We do have a raypak heater, which is currently broken and not in use, but there is visible blue copper residue on all the coils. Would that small amount (5-10lbs) of dichlor cause this, and is it bad to have in the pool (raise combined chlorine?).

 

[tillmac62]

Clean your test cylinder by letting it soak in bleach, then test CC again.

 

[mknauss]

The copper is probably from the heater. Though it shows your copper level in the pool may be quite high so any addition may make some come out of solution. No effect on CC.

The heater does that due to low pH. Dichlor is very acidic.

 

[SR71P52]

Thanks for the explanation of the copper, I have switched to only pure chlorine, so this shouldn’t be a further issue.

In other news, I just tested and dosed 3 gallons of liquid chlorine (10% sodium hypochlorite) to start SLAM according to pool math (to bring FC up to 14). I tested before at 1.5 FC and 6 CC.. an hour after dosing with filter running, I am at 4 FC and 10 CC. I’m not sure what’s going on here, but I would have expected a much greater rise in FC levels compared to what I am seeing. Also I am confused as to why the CC would rise with chlorine addition. Any ideas?

 

[Flying Tivo]

Keep rising it to Slam level. Keep testing every hour until it starts to hold, then every few hours. Use the 10ml sample to save on reagents.

 

[crimson avenger]

Keep rising it to Slam level. Keep testing every hour until it starts to hold, then every few hours. Use the 10ml sample to save on reagents.

Don’t you mean use the 5 mL sample to save on reagents? The 10 mL sample is the usual volume.

 

[SR71P52]

I added 3 more gallons and tested again after one hour.
FC: 4.5
CC: 16

I don’t know whats going on, but this doesn’t seem accurate to me? Maybe the FC is reading as CC somehow? I have been adding sodium hypochlorite liquid chlorine.

 

[mknauss]

That level of CC is very unusual. Normally only see that with addition of non-chlorine 'shock' or possibly ammonia in the water.

Just focus on FC. I would not even bother testing CC right now. Just uses reagent.

 

[SR71P52]

That level of CC is very unusual. Normally only see that with addition of non-chlorine 'shock' or possibly ammonia in the water.

Just focus on FC. I would not even bother testing CC right now. Just uses reagent.

the problem is I’ve added 6 gallons of liquid chlorine, which should have risen my FC by 30 according to pool math. Maybe my dpd test is faulty?

 

[mknauss]

If the powder is not dark purple and clumpy your test should be fine.

You are fighting some kind of organic. Chlorine is the only solution to that.

 

[SR71P52]

If the powder is not dark purple and clumpy your test should be fine.

You are fighting some kind of organic. Chlorine is the only solution to that.

This is what my dpd powder looks like.