SWG Not Keeping Up - Light green algae on surface and corners

sagosto

Well-known member
May 28, 2019
142
Mahwah, NJ
I live in North Jersey and the pool has been sparkling all year long but we've hit a span of 8-12 days of 85-95F with little rain so I have been supplementing hose water every 4-5 days to maintain water level. I typically maintain a good FC/CYA level but last few weeks I've been adding a bit of liquid chlorine as the pool has had heavy use and the sun has been heavy. Last year, I kept the SWG at 80-85% but I've been at 90-98% this year but it's been hotter. Or, am I compensating for a failing SWG?

A day or so ago, I noticed a tad bit of green in one corner of the pool a few days ago which I brushed. Today, around 6PM I've noticed quite a bit of surface green algae on sides and corners which I brushed and added 3G of 10% liquid chlorine and I am leaving the pump on all night. It's been hot and the pool has been heavy used from Sat-Monday for 6 hours each day with multiple adults and kids (PEE!). The water still looks good but the algae is concerning as I dropped FC overnight and the FC isn't holding with the SWG nearly all the way at 100%.

Please see timeline below:

July 11th @ 4PM
TA 70PM
SALT 3400PM
TEMP 81F
PH 7.6
FC 3.5
CYA 60PPM
NOTES: Don't remember if any chlorine was added

July 16th @ 4:24PM
TA 70PM
SALT 3200PM
TEMP 82F
PH 7.6
FC 5.5
NOTES: Don't remember if any chlorine was added

July 16th @ 9:53AM
TA 70PM
SALT 3200PM
TEMP 79F
PH 7.5
FC 4.0
NOTES: Don't remember if any chlorine was added

July 19th @ 12:50PM
FC 6.5PM
NOTES: Don't remember if any chlorine was added

July 20 @ 5:31PM
FC 4PPM
SALT 3200PM
CYA 50PM
TEMP 85F
NOTE: Added 1GAL of 10% liquid chlorine and cya

July 21 @ 5PM
FC 5.5PPM


July [email protected] 9:52AM
FC 4.0
SALT 3100PPM
CYA 75PPM
TA 60PM
PH 7.4
TEMP: 84F
NOTE: Added 3GAL of 10% liquid chlorine and noticed surface green algae and FC dropping from 5.5PPM to 4.0PM from previous 5PM reading
 
Last edited:

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,407
Northern NJ
You will not fix your algae problem adding an extra gallon or two of liquid chlorine. You need to follow the SLAM Process step by step with no shortcuts.

You will go through quite a bit of liquid chlorine and the SLAM Process may take two weeks or more before you meet the 3 exit criteria.

There are no shortcuts to getting algae free pool water.
 

sagosto

Well-known member
May 28, 2019
142
Mahwah, NJ
Lastly I’m familiar with process. I added all chlorine on hand at time and will get more.
However, pool looks fantastic this morning. Do I still continue with SLAM if no trace exists?

Lastly, CYA at 50 and a FC above 4 ppm is higher than target Albeit a bit low for SWG. So why light algae and daily drop off? CYA was increased days ago yet FC dropped off bringing CYA/FC out of sync even as I added chlorine to compensate for the immediate CYA increase.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,407
Northern NJ
FC drop confirms you still have algae that is consuming the chlorine.

What is your FC level?

How often are you testing and maintaining SLAM FC level?

Are you brushing the entire pool at least twice a day?
 

sagosto

Well-known member
May 28, 2019
142
Mahwah, NJ
FC has been slowly dropping for days and only light green yesterday after cya was raised. Crystal clear water and all chems looked good until cya was raise and the cya/fc got out of wack. Until recent raise to 75cya, I was at 50cya and FC 4.5 to 5.5. Could be coincidence but odd.

Check chlorine and FC every other day. I brush every other day give or take and I use robot daily.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,407
Northern NJ
FC has been slowly dropping for days and only light green yesterday after cya was raised. Crystal clear water and all chems looked good until cya was raise and the cya/fc got out of wack. Until recent raise to 75cya, I was at 50cya and FC 4.5 to 5.5. Could be coincidence but odd.

Check chlorine and FC every other day. I brush every other day give or take and I use robot daily.
I don't know what you are not understanding:
  • Alage grows in clear water
  • You don't see the initial signs of algae
  • Once you start seeing the green algae bloom the algae has been silently multiplying in your pool for days or weeks.
  • Algae has taken days or weeks to grow in the water and will now take days or weeks to eradicate
  • Chlorine consumption an early indicator and the best test of the presence of algae. That is why we do the Overnight Chlorine Loss Test
  • Somewhere alone the way despite all your diligence you let the FC level drop to low and the algae too hold

Your story is typical of an algae problem.
 

sagosto

Well-known member
May 28, 2019
142
Mahwah, NJ
This forum has a reputation for being a bit snarky but that's OK -- I need the help.

I'll explain again.

CYA 50 / FC of 4.0 (typically 4.0-5.5) is aligned with the CYA/FC guidelines per the forum. Yes, it's a bit lower than SWG guidelines but after that was RAISED along with the FC, algae was visible. You are correct -- it could have been growing in clear water but the chem test and the guidelines suggest that algae should not grow. Yes, this could also explain why the FC is dropping but I was more concerned with SWG issue as the CYA/FC were aligned.

7/23 @ 11:55AM
FC 15.0
TA 6.0
PH 8.0

Should I address PH now or wait a bit? The water level is starting to get low which will impact FC and PH (and others) but not sure how long I should wait as I probably only have 1-3 days before I am below skimmer.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,407
Northern NJ
I am not being snarky, but I am being direct.

Do you want to discuss water chemistry theory or do you want to fix your algae problem?

You think you did all the right things with your water chemistry. The algae says you didn't and it beat you and its there. We can discuss how you not get into this situation again after you get algae free water.

7/23 @ 11:55AM
FC 15.0
TA 6.0
PH 8.0
If you think you are now in the SLAM Process then you are not following it step by step with no shortcuts.

First step is to lower your pH. Did you do that?

Your last CYA you posted above is 50. SLAM FC for CYA 50 is 20. You are way off from that.

Once you are in the SLAM Process you only test FC, CC and occasionally CYA. The pH test is invalid once FC is above 10. So your pH test with FC of 15 is likely invalid.

Add water as needed to replace evaporation. The FC level will be adjusted during your regular chlorine checks as part of the SLAM Process. Your pH doesn't matter and can't be tested during the SLAM Process.

Turn off your SWG during the SLAM Process and just use liquid chlorine. Once you are algae free, you can check your salt level, turn on your SWG, and we can discuss how you maintain your FC/CYA.

The more often you check your FC and raise it back to SLAM FC level and brush your pool the quicker the SLAM Process will get done.
 
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sagosto

Well-known member
May 28, 2019
142
Mahwah, NJ
PH was 7.4 so there was no need to lower it. I am off to get more liquid chlorine. The FC dropped from 15PPM to 9.5PPM, CC of 0, and the water is crystal clear. I will do a OCLT tonight. The mesh screens in the robot showed no green at all which was very surprising.
At least 2 out of 3 SLAM exit criteria has been met. Maybe I'll get lucky? :)

July 23 @ 4:20PM
PH 7.8
FC 9.5PPM
CC 0
 

sagosto

Well-known member
May 28, 2019
142
Mahwah, NJ
FC was 13.5 at 9pm ish last night and 12.5 at 830am this morning. No direct sunlight but light out.

All 3 exit criteria have been met after 1 day and lower FC due to lack of chlorine in my area.