Clear water but dropping FC

Jump to latest Follow Reply
RedScare

RedScare

0
Gold Supporter
Silver Supporter
Feb 1, 2015
105
The Woodlands TX
Pool Size
12000
Surface
Plaster
Chlorine
Liquid Chlorine
Hello everyone!

My situation is pretty much the way the title sounds. Last week, after a winter of only occasional attention, I noticed my pool had some slight green along the walls and floor. I ran the numbers, and they came out looking like this...

FC - 0
CC - 0
pH - 7.8
TA - 70
CYA - 30

I poured 121 oz Clorox 8.25% in the pool, and brushed the sides and bottom. I also vacuumed. Each of the next 3 days I added one bottle of Clorox. The FC would come in around 10 to 12, CC at 0.5. Within a day or so, the pool became clear, and the green disappeared. All good so far.

I ran the OCLT each of the last two evenings, and I am losing about 1.5 each time. Specifically, last night my reading was 10.0, CC 0.5. This morning I was at 8.5 and 0.5. This afternoon, I tested and got FC 6.0 and CC 0.5. The pool still looks clear with no green accumulation. I also backwashed the filter this morning.

Should the high chlorine drop in the OCLT concern me? Everything looks good, and the numbers are close, but not perfect. What do you think?
 
Red, don't let the clear water fool you. It looks to me as though you simply need to employ a "SLAM" and knock that algae out for good. Simply adding one gallon of bleach each day won't do it. You'll need to "maintain" the required SLAM FC level until you pass all 3 SLAM criteria. With a CYA of 30, your SLAM/Shock FC level should be maintained at "12" - 24 hrs per day until the SLAM is complete. If everything is done as noted on the SLAM page (link below in my sig) you should do just fine. Let us know if you have any more questions.

Oh - don't forget to lower the pH to 7.2 - 7.5 before raising the FC to 12 for the SLAM.
 
My pool is also 12,000 gallons and if my FC were zero, one gallon of 8.25% liquid chlorine would only bring it up to about 7.5 of FC.

18 ounces=1ppm FC in my pool.

You never had your FC high enough to actually kill all the algae. Please review the SLAM directions.

Let us know how it goes :)
 
I probably used the wrong term in saying "afraid". After 8 months of reading this forum, and doing my own chemistry and maintenance, there is literally nothing about this pool that scares me...thanks to everyone here. :)

OK, so last night I added 60 ounces of muriatic acid to reduce the pH in preparation for the SLAM this morning. This morning, my numbers looked like this...

FC - 14
CC - 0.5
pH - 7.2
CYA - 22

I was a little surprised that my CYA had dropped further, but we did get a lot of rain last week. Should I do anything about the CYA now during the SLAM? Should I do anything to raise it once my SLAM is complete? Everything else looks to be pretty good.

- - - Updated - - -

YippeeSkippy said:
My pool is also 12,000 gallons and if my FC were zero, one gallon of 8.25% liquid chlorine would only bring it up to about 7.5 of FC.

18 ounces=1ppm FC in my pool.

You never had your FC high enough to actually kill all the algae. Please review the SLAM directions.

Let us know how it goes :)
Click to expand...


You are correct. The first gallon took it to 7-7.5. The next day, an additional gallon took it from 5.5 to 12. Last night, I added one gallon to the existing 6.0 level, and this morning I am at 14. So, the numbers seem pretty consistent with what you predicted.
 
I would get enough CYA in the pool to get it to 30, but only just enough. It could be a testing error as the CYA test is a bit subjective and can vary based on the lighting when the test is performed. Consider retesting before adding CYA. Once you complete the SLAM, I'd certainly get the CYA up to 40 or 50 based on your location. Rain won't drop your CYA by that much either. If the test was accurate, you lost 8 ppm CYA. In order to accomplish that, you'd have to replace 25% of your water.
 
I believe I have some trichlor tablets left over from my auto chlorinator days. Would you recommend running that for a few days after the SLAM is complete to boost CYA? Or, is their some other method that works better?
 

Enjoying this content?

Support TFP with a donation.

Give Support
When increasing CYA, it's best to use just pure CYA. Check out Pool School - Recommended Pool Chemicals and the details on CYA and how to add it to your pool.

Save the pucks for when you go out of town for a few days and have wiggle room with your CYA. Pure CYA can be bought at many big box stores that have a pool section. HTH is my favorite brand so far as it has finer granules that dissolve faster.
 
I'm using the tube in the TF100 kit. The level did not quite reach the 20 mark. I estimated it to be at a 22 if the tube had markings that precise.

- - - Updated - - -

I did not get a chance to test yesterday evening. My last test was at 3:30 pm, with an FC level of 12. This morning, FC came in at 11. I will do an OCLT this evening to see how it looks.
 
RedScare said:
I'm using the tube in the TF100 kit. The level did not quite reach the 20 mark. I estimated it to be at a 22 if the tube had markings that precise.
Click to expand...
You can't make assumptions like that. The scale on the tube is not linear so you can't say that half way between 20 & 30 is 25. Always round up for FC/CYA calculations, so in your case SLAM for a CYA of 30.
 
I see. Speaking of chemistry interpretations, when testing the chlorine level, I have noticed that after letting the water sit for several minutes the previously clear water returns to a shade of pink. Is this a normal reaction? The water had been clear at the time of testing. It is only after sitting for at least a couple of minutes that the solution turned pink again.

BTW, this evening's test came in at 11. So, only a drop of 1 ppm all day, after a drop of 1 ppm overnight. This looks very encouraging. Water is still clear.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply