How would you interpret this? Algae?

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C

chris-md

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Jul 28, 2017
37
Silver Spring, MD
Hello everyone!!

Third year with our freshwater chlorinated pool! First year was a nightmare with algae, but last year was really good.

I think this third year we may be having more algae issues but I wanted to get your opinion on this. What I’m seeing Is not quite making sense to me.

Two issues experienced for the last 2 weeks:
I’m experiencing MASSIVE chroine demand during the day, drops of 15ppm or more of FC...
Overnight chlorine loss stands at MAYBE 1ppm
very cloudy pool (partly from the shock I’m sure, but not completely)

Here are my parameters (currently SLAMming the pool):

FC: 30 ppm, will drop to 12-20ppm between 7am-6pm, spiked up to 30ppm in evening, rinse and repeat
CYA: between 40-50
CH: 350ppm - using cal hypo right now for shock but will be up to 400ppm when this bucket is empty so will have to switch over to something else)
TA: 100ppm
pH: 7.4 last measured before hyperchlorination
Water: water is cloudy, but still blue. Again, I’m sure partly due to the cal hypo, but it was cloudy before I started shocking.

No ammonia present. CYA over winter did drop to zero, so added more 2 weeks ago and just this evening tested for it to make sure.

So, my question: What is going on??
Does this sound like algae?
The drops I’m seeing seem more like lack of CYA than algae...would algae bloom give me such huge chlorine drops??

I’ve been hyperchlorinating and keeping it that way for 2 weeks with no change - daily brushing also. Not sure what else I can do.

Any advice???
 
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The drop is due to you greatly overshooting SLAM level. Nothing surprising about losing 50% of your FC during the day when keeping FC levels at nearly 100% your CYA level.
 
Does not sound like algae as the chlorine demand would be constant and not based on the time of day.
Agree that losses are likely due to the sun ... although you might be thinking about this wrong ...

The CYA will effectively protect a % of the chlorine from the sun. So the higher you raise the FC, the more PPM will be lost to the sun.
Say hypothetically that at a CYA of 50ppm, 50% of your FC is protected.
Starting at 30ppm, you will lose 15ppm to the sun.
Starting at a FC of 7ppm, you would only lose 3.5ppm.

Stop using cal-hypo which may be the cause of your cloudiness and use liquid chlorine.
 
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Thank you guys. That sorta makes sense to me. So what should my next step be? Let it drop down low (i dunno, <10ppm) and see what the demand is at that point?

I should mention: for several days, I would only get it up to about 20ppm if I was lucky, and even then got drops down to 12, then down to 1-2ppm. This is why I took it way up to 30ppm.
 
Yeah, don't do that. There is a reason that the FC levels we recommend exist. Going too high can damage the pool or equipment.

So what are you CC levels?
Have you passed the OCLT?

If you are down to residual cloudiness, I would switch to bleach from the cal-hypo and see if that quickly resolves it.
 
Thanks for your guidance, really appreciate it.

CC is around 0.5 (never seen it higher than that before).

I occasionally pass OCLT, but it’s not every night, maybe half the time (given the losses during the day I’ve kept watching it, even when it’s been zero). Usually lose 1-1.5 ppm, but there have been nights where I’ve lost nothing at all.
 

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