To SLAM or not to SLAM

[DjGill]

My pool is clear with the following readings

FC near 0
ph 7.2
TA 70
CYA 80
Hardness 400

I've tried chlorinating with liquid chlorine (@ 121 oz) but I am unable to get a reading. Why isn't the generous addition of chlorine making a difference? Do I need to SLAM despite no visible evidence of algae?

 

[Texas Splash]

Do I need to SLAM despite no visible evidence of algae?

Can't confirm that just yet, but it's a possibility. One gallon of 10% chlorine in your 21K pool should be about 4.5 ppm of FC. Seems like it should be enough to show something, but if you have something brewing, that chlorine may get used-up really fast. Is your test kit fairly new? Are you using the FAS-DPD (powder & drops)? If so, then I'd add another gallon, maybe even two gallons (about 9 ppm) which is fine since your CYA is 80. The FC has plenty of room - see FC/CYA Levels. Let us know if you get something to show.

 

[DjGill]

Thanks Texas. I purchased my kit a couple of months ago, and I did use the powder and drops. I ended up SLAMing and was able to get chlorine readings, though still a bit low. My high CYA is a bit of a problem too, so I will try to keep the chlorine levels higher while draining and refilling the water as much as is practically possible!

 

[Newdude]

Hey Gill and belated welcome !! If it’s a one off problem it’s possible that your bleach sat out in the sun at the store and degraded, or it was older stock to begin with.

other than that, your *exact* post comes up frequently and the answer to ‘do I need to SLAM’ almost always is yes. Algae grows exponentially so it can sit right on the edge of a full explosion, but just below where it becomes visible. If your chlorine is full strength, something is using it up.