Chlorine Levels in relation to CYA Question

[Tjruss]

Moved from here.. Chlorine Levels in relation to CYA

Hi all - I’m a newbie to TFP and just switched from tabs to a SWG this season. Water looks and feels great. CYA is around 25 and FC is between 1&2 (R2006c test kit on the way so will get more accurate reading) and Combined Chlorine is between 3&4.
pool store is telling me I have a chlorine lock.
question - will raising my cya and my FC a bit level things out or do I need a SLAM? And is it normal to need a SLAM this early in the season? As I mentioned, the water looks great.

 

[Texas Splash]

Welcome to TFP! Chlorine lock is a bad term - a myth really. Something used for those who don't understand the FC/CYA relationship. Pool stores are some of the worst. Basically you need the FC to balance to the current CYA as noted on the FC/CYA Levels to avoid algae. Not all algae is visible. When you get your test kit, post a full set of numbers and we'll show you just how accurate your testing is and what it means. Great to have you with us.

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Your one-stop shop for all things TFP to include: ABCs of Water Chemistry, Recommended Chemicals/Levels, Test Kits, Troubleshooting, and much more!

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[Texas Splash]

Oh, and also be sure to update your signature with all of your pool and equipment info. Be sure to include which test kit you ordered (TF-100 or Taylor K-2006C) as well.

 

[Tjruss]

Ok TFP experts, I’m baffled. 21 year old pool with historical use of tabs and powder shock. Started having some algae issues the last 2 years so decided to switch to liquid Chlorine (based on TFP recommendations). Things seemed to stabilize. Then this year decided to switch to SWG and installed Circupool RJ-45 in my 20000 gallon vinyl pool. Opened the pool this year and balanced water and everything looks great. Water is crystal clear and no signs of algae. But started loosing FC.
Got my K-2006c kit and did some testing. Initial results:
FC = 0
CC= 0
CYA = 0
TA = 50
PH = 7.2

So I’ve got my CYA up to 50 now and I’ve been adding chlorine based on Pool Math calculations. So far I’ve added 3 gallons of 12% Liquid chlorine over the past 4 days. Still 0 FC reading. I did pull a sample directly from return line and my SWG is generating chlorine and have had it set to Super Chlorinate mode for the past 24 hours. Still FC of 0 this morning. Wanted to get some input before I dump another case of chlorine in.
thanks for reading my long post and for any advice!

 

[clambert1273]

Off the top of my head, couple of things

1. Chlorine is a consumable and will be used daily whether its stuff in water or sacrificed to UV

2. Swg's are for maintaining a pool that presumes nothing in the water growing

3. You probably need to do Overnight Chlorine Loss Test

if oclt fails then SLAM Process

for now if it was me, I would add liquid chlorine to about 6 for now then do the oclt

 

[Texas Splash]

Our situations are almost identical. RJ-45, my pool almost 18K. One gallon of 10% is about 5 ppm of FC for me, slightly less for you. I agree with Christina. Add chlorine ASAP. Our SWGs are not designed to make such a large increase that fast. I would add 2 jugs now, and re-test in about 1-2 hours. Keep the FC in that 8-10 range then do an OCLT tonight with the SWG off. I suspect you already have algae going, but you'll OCLT will confirm.

 

[Tjruss]

Back again. Did the OCLT - last night FC was 4.0 and this morning was back to 0. So I guess a SLAM is in order. I am questioning the potency of my liquid chlorine. The box was stamped with 052121 on the box, which I assume is a manufacture date, so should still be ok. I put a gallon of 12% in yesterday AM and it was cloudy skies all day. Then added another after sundown and still only got to FC of 4ppm. May try a different source.
Water is still crystal clear, but I guess a SLAM will fix whatever is going on.
Question - how much does the powder dichlor or cal-hypo raise cya? My CYA is at 50 currently. I’ve had much better luck in the past boosting FC with powder in the past.

 

[Oly]

The solid products are adding more than just chlorine and that complicates things for you. Adding dichlor will raise your CYA and drive up the amount of FC needed to SLAM and maintain. Adding calhypo will raise your calcium levels. Best to use liquid and focus only on control of the algae now.

 

[Sunnydaze]

Back again. Did the OCLT - last night FC was 4.0 and this morning was back to 0. So I guess a SLAM is in order. I am questioning the potency of my liquid chlorine. The box was stamped with 052121 on the box, which I assume is a manufacture date, so should still be ok. I put a gallon of 12% in yesterday AM and it was cloudy skies all day. Then added another after sundown and still only got to FC of 4ppm. May try a different source.
Water is still crystal clear, but I guess a SLAM will fix whatever is going on.
Question - how much does the powder dichlor or cal-hypo raise cya? My CYA is at 50 currently. I’ve had much better luck in the past boosting FC with powder in the past.

How long was it between adding the gallon last night and testing at 4ppm? You're losing a good amount of chlorine to algae (at least 4ppm overnight) and 1 gallon of 12% in your pool would increase your levels by 6ppm. If you waited a couple hours, I'd think 2ppm could have already been consumed.

Stick with liquid chlorine.

 

[jmikeb]

is your cya still at 50 or did it disappear too?

 

[Tjruss]

How long was it between adding the gallon last night and testing at 4ppm? You're losing a good amount of chlorine to algae (at least 4ppm overnight) and 1 gallon of 12% in your pool would increase your levels by 6ppm. If you waited a couple hours, I'd think 2ppm could have already been consumed.

Stick with liquid chlorine.

Tested about 45 minutes after adding it around 10:30pm. If algae was eating that much FC, wouldn’t it be a little visible? Pool water sparkles...

 

[Tjruss]

is your cya still at 50 or did it disappear too?

CYA seems to be holding steady around 50.

 

[magiteck]

Back again. Did the OCLT - last night FC was 4.0 and this morning was back to 0. So I guess a SLAM is in order. I am questioning the potency of my liquid chlorine. The box was stamped with 052121 on the box, which I assume is a manufacture date, so should still be ok. I put a gallon of 12% in yesterday AM and it was cloudy skies all day. Then added another after sundown and still only got to FC of 4ppm. May try a different source.
Water is still crystal clear, but I guess a SLAM will fix whatever is going on.
Question - how much does the powder dichlor or cal-hypo raise cya? My CYA is at 50 currently. I’ve had much better luck in the past boosting FC with powder in the past.

I’ve seen some LC stamped with an “expiration date” usually a year from the manufacture date. If that’s the case with yours it could be over a year old at this point. I’d try adding the LC and testing in 15 minutes to see if it’s at the level you’d expect. If it’s not, I’d bet the LC is much weaker than it’s labeled.

 

[Tjruss]

Ok - went to a different source for the LC. Ready to start SLAM. Got FC up to around 16 yesterday afternoon then it dropped to around 12 after a few hours. So added LC and got it to 20ppm (my CYA is 50 so 20 ppm is SLAM target) at 10pm.
Checked at 8am today and it’s back down 10ppm. Pool math says another 1 gal, 3 qts to get back to 20ppm. So will add that and see where we go.

Still can’t believe it’s using so much chlorine when the pool is so clear and everything else is in line. I guess this is where that patience aspect comes in...

Let me know if you think I’m missing anything.

 

[clambert1273]

Sounds like you are doing good! The more you can test and add then the faster the chlorine starts to hold longer, make sure you are brushing real good while at slam levels

 

[Bperry]

Ok - went to a different source for the LC. Ready to start SLAM. Got FC up to around 16 yesterday afternoon then it dropped to around 12 after a few hours. So added LC and got it to 20ppm (my CYA is 50 so 20 ppm is SLAM target) at 10pm.
Checked at 8am today and it’s back down 10ppm. Pool math says another 1 gal, 3 qts to get back to 20ppm. So will add that and see where we go.

Still can’t believe it’s using so much chlorine when the pool is so clear and everything else is in line. I guess this is where that patience aspect comes in...

Let me know if you think I’m missing anything.

If your chlorine level was zero for any length of time (and it sounds like it was) algae can get started well before you start to see it.

 

[Tjruss]

Just thought of something. My pool light went out so I opened it a couple weeks ago to check what replacement I needed. The light housing was filled with what looked like dead algae. Wouldn’t the sanitizer kill anything in the light housing as well as the pool water?
Wondering if this is the source of my problem. I’ll get in there later today to clean it out and will also backwash DE filter (if it ever stops raining).
Is there any concern going in the water at FC levels around 20ppm?

 

[clambert1273]

Just thought of something. My pool light went out so I opened it a couple weeks ago to check what replacement I needed. The light housing was filled with what looked like dead algae. Wouldn’t the sanitizer kill anything in the light housing as well as the pool water?
Wondering if this is the source of my problem. I’ll get in there later today to clean it out and will also backwash DE filter (if it ever stops raining).
Is there any concern going in the water at FC levels around 20ppm?

Nope go ahead and clean it out while the levels are high, might be good to leave it sitting on deck if possible until slam is done

 

[DorsalSpine]

A light housing doesn't see much if any circulation. So it can be a breeding ground for algae. Opening it up and letting your high LC water in will do the trick.

 

[Tjruss]

Good morning TFP! Just tested at 7am and FC is at 10ppm down from 19ppm at 8pm last night. Looks like it’s back to the pool store for more LC. I’m in for about 20 gallons so far. My recycling guys are going to think I’m running a chem lab or something.
I did clean out the light housing and will backwash the DE filter this morning. Hopefully it starts to stabilize today. Its supposed to be full sun today, so will need to check more frequently.
Thanks for all the feedback!