Sunlight, Slamming and CC

[Sailracer]

Hi All,

I have been SLAMming for a week to deal with a mustard algae outbreak and am getting inconsistent results. The pool has been clear for a few days, but chlorine usage is inconsistent. For example, last night before bed I had

FC: 28
CC: 2
PH: 7.6
TA: 90
CYA 70

In the morning I had
FC: 27.5
CC:2

I added a gallon of 12.5% bleach and tested a couple hours later (pool in sun):
FC: 28
CC: 0

I then tested this evening and had:
FC: 22
CC: 2.5 (kids went swimming for an hour could that cause this much CC? Other days with no swimmer load also have had CC go up)

Questions:
Why didn't FC or CC drop overnight? I would've expected the FC to burn off the CC. If living algae were still present, I would've expected FC to drop.
Could algae still be growing at these FC levels and still causing CC?

 

[ajw22]

CC does not drop overnight; FC does not burn off CC.

Daylight sun UV burns off CC.

Yes, you still have algae causing the CC unless you are adding a chemical causing CCs.

CC - Further Reading

www.troublefreepool.com

 

[Sailracer]

Thanks for the info. I'm starting to think the overnight FC not dropping was a fluke reading that one night. It dropped from 29 to 26 last night and I still have CC at 2.5, so that all indicates the chlorine is still working on something.

 

[Sailracer]

I'm still struggling here- it seems like something is wrong and I am making no progress here and throwing money down the drain continuing to SLAM. My pool is clear. I have no signs of algae- there is no dead algae or "dust" accumulating on the bottom of the pool anymore. Nothing seems to be stirred up when I brush. I have removed the lights and scrubbed the niches. I've backwashed. Vacuumed to waste. But still chlorine demand is high and CC is staying high. Last night FC dropped from 29.5 to 26 and CC went from 1 to 2. That wasn't too much drop, so I was hopeful maybe chlorine demand was going down and the sun today would burn off the CC and I would be good. I added 2 gallons 12.5% chlorine (should add 8.3ppm) in the morning and tested this afternoon and FC was down to 19.5 and CC was up to 2.5. Very disheartening- demand seems to be going up even more.

Could this be something else other than algae? There is residual salt in the pool from back when I had a SWG. I have added over this season: Trichlor tablets, Calcium Hypochlorite shock, Calcium Chloride, baking soda and 12.5% liquid chlorine.

I added well water in the middle of the process after vaccuming to waste. That always tints the pool green immediately, I assume because of iron. The green went away after a day or two. Could well water introduce algae or something else?

Could the solar panels be harboring algae or eliminating the effectiveness of the chlorine going through it? Would that explain why my CC is going up more during the day than the night? I have tried bypassing the solar panels this afternoon to see if it makes any difference.

Could my chlorine be bad? Would bad chlorine cause CC to rise when adding it?

Could my test chemicals be bad? Would they cause false high readings? I would've expected the other way around. I have confirmed with test strips that they see CC present as well. If my CYA reading were falsely low and much higher than 70, would I expect the chlorine to still be "working" and creating CC from the algae?

 

[ajw22]

How about posting some pictures of your pool and equipment?

Could my chlorine be bad? Would bad chlorine cause CC to rise when adding it?

No. Chlorine will lose effectiveness and degrade to water.

Could my test chemicals be bad? Would they cause false high readings?

No. If test chemicals lose potency they are will read lower then actual.

Could well water introduce algae or something else?

No telling what could be in well water if it has not been tested. When did you last have your well water tested?

Could this be something else other than algae? There is residual salt in the pool from back when I had a SWG. I have added over this season: Trichlor tablets, Calcium Hypochlorite shock, Calcium Chloride, baking soda and 12.5% liquid chlorine.

Those things do not consume chlorine. There are chemicals like algaecides that contain ammonia that can consume chlorine.

@mknauss any ideas?

 

[mknauss]

Clean your test vial really good with bleach and rinse it out. Sometimes that will create erroneous CC levels.

On the OCLT, let the FC drop to 20 ppm or under and do the OCLT. Higher level FC OCLT can be difficult as the error rate of the test is about 1 drop in 10. At 29 ppm you are at nearly 60 drops.

 

[Sailracer]

Thanks for the suggestions. Other pretinent info- the pool was replastered last summer. The chlorinating ducks in the photo below are removed during the night when I am doing the OCLT.

Here are some photos.

The pool (with my test kit and 10ml pipette for accurate filling of the test tube)


The equipment:


The solar panels:


The clarity of the main drain (9.5ft down):


Telephoto zoom of the drain through 9.5 ft of water:


A sample of some weird black-ish stains I have seen lately that don't scrub off:

 

[Sailracer]

Clean your test vial really good with bleach and rinse it out. Sometimes that will create erroneous CC levels.

This may be the culprit! I just soaked the test vial and pipette in bleach for a few minutes and rinsed them out- the test vial showed kind of a yellow discoloring after that, so I got out a scrub brush and scrubbed the inside of it out really well, rinsed it again and took my evening measurements and had 0 CC!

 

[mknauss]

Great. Do realize your duck floater with trichlor in them are constantly raising your CYA level, which means you need a higher FC level.

 

[Sailracer]

I passed the OCLT with .5ppm of chlorine loss and 0 CC last night, so I think that confirms the test tube contamination was the problem. Thank you for that suggestion!

I am aware the trichlor adds CYA. I keep an eye on it. It was up at 80 at the end of last season when my SWG kicked the bucket. With my short swim season and partial draining of the pool every Winter I am hoping it continues to slowly go down overall.

Edit- I got into the situation of needing to SLAM through stupidity. For some reason at the start of this season my memory failed me and I was calculating my chlorine levels based on 1 drop = 1ppm with a 10ml sample instead of .5ppm, so my chlorine levels were maintained at half what they needed to be. I didn't catch that error until after I started the SLAM and it seemed like I was getting higher FC levels from a gallon of shock than the calculator suggested. It was only then that I caught my mistake.