Algae will not die perfect water readings?

[Mom2howmany]

Ok, I have a small 6000 gallon above ground pool. I have a swg and sand filter but my salt cells died so it turned green. With spring coming I’ve ordered new cells and need to kill the algae.

so my cya is low, at 20 but I don’t want to raise it while slamming thinking it’s cold and not too sunny here so I don’t need a high cya since chlorine level would drop slower. So leaving it at 20 let’s me have a lower fc level?

my ph is 7.4

heres the thing, my fc has been at 10 for days. It doesn’t drop even over 24 hrs yet the algae isn’t dying? Or at least I don’t think it is. Typically when algae dies it sinks and you vacuum it up, right? My water is green, no sinking algae and zero improvement in the water. Water temperature is cold so I’d expect the fc to not drop very quickly but with all the algae I’d expect it to at least drop until it’s clear. Or at least get water improvement. I’ve backwashed and the filter is definitely filtering out a ton of algae so I would think is working properly, my pressure is fine. So why isn’t it dying off?

 

[Mom2howmany]

If it matters, my salt is at 3400, ta 80, borates approx 15

 

[Texas Splash]

Well, let's exchange some info to try and get you a solution:
- Which test kit are you using? Might also consider updating your signature with all of your pool info to include the kit for future reference.
- Yes, a lower CYA allows for a lower FC, however the CYA test doesn't provide complete accuracy below 30, just like it's not accurate over 100. So to be safe, you should ensure the CYA is at a solid 30 for now.
- The fact that you are fairly certain you have algae, are actively filtering some out, yet it's still there tells me either the FC or CYA (or perhaps both) are off a bit. When the chlorine is at the proper SLAM level for the current CYA, algae has to react in some way (getting lighter green, white, grey, etc).
- How cold is your water? If it's below 60, the CYA test might not be accurate. With cold water, it's best to bring the sample inside for about 30 min to let it warm up, then go back out and read it under the sun. That might influence your CYA number.
- It's also possible you have some algae hiding somewhere that it's thriving. Do you have steps or a ladder in the water? Now might be the perfect time to remove anything in the water (if there) to inspect/clean it.
- Just to be sure, how are you increasing your FC right now? Bleach? Anything else been added to the water?

With this exchange maybe we can confirm or eliminate some issues for you to consider.

 

[Mom2howmany]

its a blue devil testing kit.

i retested after leaving in the house, same results.

there are no ladders or anything in the pool currently.

i am using bleach.

Though now that I think of it, I did toss in trichlor shock weeks ago when it first turned green since at that time my cya tested at 0 so I figured raising the cya wouldn’t hurt anything. Apparantely it must mess with more than your cya. Am I doomed and have to drain?

 

[tim5055]

We base our pool care system on accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. The Blue Devil (OTO) test kit is not accurate enough for a SLAM Process

Order a TF100 test kit and at least include the XL option. That will give you what you need while you are clearing the pool, and probably enough reagents for a couple of years normal use.

While you wait for it to get delivered, you have a homework reading assignment. Start with ABCs of Water Chemistry and Turning Your Green Swamp Back into a Sparkling Oasis