Zara Nazir
Member
I want a specific range where efficiency suddenly fails.
Is there a threshold CYA level where chlorine effectiveness drops dramatically?
- Thread starter Zara Nazir
- Start date
Ionut Kaminski
Member
For me there isn’t one magic CYA number where everything suddenly collapses, it’s more that higher CYA demands a higher free chlorine level to keep the active ratio strong. The “dramatic” drop happens when you keep the same low chlorine target while CYA has climbed, then the pool starts smelling off, clears slower, or algae shows up easier. Practically, I tie my chlorine target to my CYA level instead of chasing one fixed chlorine number.
Amira Mansor
New member
Generally, higher CYA levels demand more chlorine to maintain the active ratio, but there’s no specific number where everything “suddenly fails.” With higher CYA, sanitizer tends to drop faster, so I prefer adjusting chlorine levels according to CYA rather than chasing one fixed chlorine number. So, with high CYA, make sure free chlorine stays high enough to prevent the water from smelling or clearing slowly.
Yuto Shen
Member
In my opinion, there isn’t a single CYA level where chlorine suddenly “fails.” The drop in effectiveness is gradual because higher CYA reduces the active chlorine fraction. It feels dramatic when CYA climbs (around 80–100+ ppm) but free chlorine isn’t adjusted accordingly. So it’s not a hard threshold it's a balance issue between CYA and free chlorine.
Leon De Vries
Member
In my view, there isn’t a single CYA number where chlorine effectiveness suddenly collapses. The reduction is gradual because CYA binds part of the active chlorine. Issues usually show up when CYA gets high (around 80–100 ppm) but free chlorine isn’t increased accordingly. It’s not about a hard threshold—it’s about maintaining the proper FC-to-CYA ratio.
Zheng Zhou HOO CHEMTEC
New member
You'll hear different numbers, but in my experience, the cliff is around 70-80 ppm CYA.
Below that, chlorine still works, though slower as you go up. Once you cross 80 ppm, the effectiveness drops off a cliff. You'll notice you need way more chlorine to fight algae, and it feels like you're pouring chemicals in with no result (often called "chlorine lock").
For a specific range where it fails: 80 - 100 ppm. At this level, your chlorine is basically sedated, and it’s very hard to keep the pool sanitized unless you maintain a much higher Free Chlorine level than most people realize.
Below that, chlorine still works, though slower as you go up. Once you cross 80 ppm, the effectiveness drops off a cliff. You'll notice you need way more chlorine to fight algae, and it feels like you're pouring chemicals in with no result (often called "chlorine lock").
For a specific range where it fails: 80 - 100 ppm. At this level, your chlorine is basically sedated, and it’s very hard to keep the pool sanitized unless you maintain a much higher Free Chlorine level than most people realize.
John Smith
Member
I’d push back a little on the idea of a hard “cliff.”
Chemically, there isn’t a sudden failure point where chlorine just stops working at 80 ppm CYA. What happens is the fraction of hypochlorous acid keeps getting smaller as CYA rises, so the same 2 or 3 ppm free chlorine becomes less aggressive. It’s a ratio problem, not a switch flipping off.
Where it feels dramatic, in my experience, is when CYA gets above about 70 to 90 ppm and people keep aiming for a flat 2 to 3 ppm FC. At that point the active chlorine concentration is low enough that oxidation slows down noticeably. You’ll see slower algae kill times, combined chlorine lingering longer, and cloudy water taking more effort to clear. That’s when people start saying chlorine “isn’t working.”
For example, at 30 to 50 ppm CYA, keeping FC around 4 to 6 ppm gives a solid active level. At 80 to 100 ppm CYA, you may need 8 to 12 ppm FC to maintain a similar active fraction. If you don’t scale it, it feels like a collapse, but it’s really just math catching up.
Where I personally draw the line is around 90 to 100 ppm. Not because it chemically fails there, but because the required FC to stay ahead of algae gets high enough that it becomes inefficient and harder to manage. At that point a partial drain makes more sense than constantly running elevated chlorine.
So I wouldn’t call it a dramatic threshold. I’d call 80 plus ppm the range where ignoring the FC to CYA ratio starts biting you. Anyone running over 100 ppm long term without adjusting FC upward consistently?
Chemically, there isn’t a sudden failure point where chlorine just stops working at 80 ppm CYA. What happens is the fraction of hypochlorous acid keeps getting smaller as CYA rises, so the same 2 or 3 ppm free chlorine becomes less aggressive. It’s a ratio problem, not a switch flipping off.
Where it feels dramatic, in my experience, is when CYA gets above about 70 to 90 ppm and people keep aiming for a flat 2 to 3 ppm FC. At that point the active chlorine concentration is low enough that oxidation slows down noticeably. You’ll see slower algae kill times, combined chlorine lingering longer, and cloudy water taking more effort to clear. That’s when people start saying chlorine “isn’t working.”
For example, at 30 to 50 ppm CYA, keeping FC around 4 to 6 ppm gives a solid active level. At 80 to 100 ppm CYA, you may need 8 to 12 ppm FC to maintain a similar active fraction. If you don’t scale it, it feels like a collapse, but it’s really just math catching up.
Where I personally draw the line is around 90 to 100 ppm. Not because it chemically fails there, but because the required FC to stay ahead of algae gets high enough that it becomes inefficient and harder to manage. At that point a partial drain makes more sense than constantly running elevated chlorine.
So I wouldn’t call it a dramatic threshold. I’d call 80 plus ppm the range where ignoring the FC to CYA ratio starts biting you. Anyone running over 100 ppm long term without adjusting FC upward consistently?
Ananya Agarwal
New member
There isn’t a single CYA number where chlorine suddenly “falls off a cliff”, it’s a gradual effect: as CYA rises, a smaller fraction of chlorine stays active, so the same FC feels weaker. The “sudden failure” feeling usually shows up when CYA is already high (often starts getting annoying around 70–80 ppm and gets worse at 100+ ppm) but FC is still kept at the old low target, then you see musty smell, slow clearing, or algae popping up. For real stability, don’t chase one fixed FC number, raise FC as CYA rises, or lower CYA with partial water replacement if it’s climbed too far.
Zara Nazir
Member
Thanks everyone, your replies were really helpful. I understand now that this is not about one exact number where chlorine suddenly “fails,” but more about its effectiveness gradually dropping as CYA increases, so the key is really keeping the FC/CYA balance right instead of chasing one fixed chlorine number. I really appreciate all the explanations and shared experience.
Jason Bennett
Member
Yeah this thread already nailed the “no hard cliff” part, so i’ll just throw in where it actually started feeling like a problem for me in real use
For me the tipping point wasnt a single number, but once my CYA crept into the 70-80 range, i had to stop thinking in terms of normal FC targets completely. I was still aiming for around 3 ppm out of habit, and that’s where things quietly started slipping. Water looked fine in the morning, but by late afternoon it had that slightly tired look, and CC would hang around longer than usual after any heavy use
What made it feel like a sudden drop was the lag in response. Like brushing didnt “wake up” the pool the same way, and oxidation just felt slower overall. Once i pushed FC higher to match the CYA, things snapped back pretty quickly, which told me nothing had actually failed, i was just underdosing for that stabilizer level
One thing i dont see mentioned as much is how this affects recovery time. At higher CYA, if something does go off, like a small algae patch or cloudy water, it just takes longer to bounce back unless you’re really aggressive with FC. That’s where it starts feeling inefficient, not broken, just slower and more demanding
I ended up treating around 80 ppm as my personal “line”, not because chlorine stops working, but because everything becomes less forgiving if you fall behind even a little. Curious if anyone here actually prefers running higher CYA long term or if most people just end up draining it back down once it creeps up too far.
For me the tipping point wasnt a single number, but once my CYA crept into the 70-80 range, i had to stop thinking in terms of normal FC targets completely. I was still aiming for around 3 ppm out of habit, and that’s where things quietly started slipping. Water looked fine in the morning, but by late afternoon it had that slightly tired look, and CC would hang around longer than usual after any heavy use
What made it feel like a sudden drop was the lag in response. Like brushing didnt “wake up” the pool the same way, and oxidation just felt slower overall. Once i pushed FC higher to match the CYA, things snapped back pretty quickly, which told me nothing had actually failed, i was just underdosing for that stabilizer level
One thing i dont see mentioned as much is how this affects recovery time. At higher CYA, if something does go off, like a small algae patch or cloudy water, it just takes longer to bounce back unless you’re really aggressive with FC. That’s where it starts feeling inefficient, not broken, just slower and more demanding
I ended up treating around 80 ppm as my personal “line”, not because chlorine stops working, but because everything becomes less forgiving if you fall behind even a little. Curious if anyone here actually prefers running higher CYA long term or if most people just end up draining it back down once it creeps up too far.
From my experience the magic number where things start going sideways is around 70-80 ppm. Below that you can still maintain pretty easily with normal chlorine levels. Above that and you start needing more and more chlorine to keep things under control. By the time you hit 100+ its basically a losing battle, at least it was for me.
I drain about a third of my pool and refill every spring now just to keep CYA in check. Switched to liquid chlorine too since it doesnt add any stabilizer.
I drain about a third of my pool and refill every spring now just to keep CYA in check. Switched to liquid chlorine too since it doesnt add any stabilizer.
following this because my CYA keeps creeping up and I dont really understand how much is too much. my test strips are showing around 70ish and my pool store said thats fine but I keep reading online that anything over 50 is bad. confusing getting different answers depending on who you ask
The general consensus in the industry is that once CYA gets above 70-80 ppm, free chlorine becomes significantly less effective at killing pathogens. The relationship isnt linear though. At 30 ppm CYA you need around 2-3 ppm FC to maintain proper sanitation. At 80+ you need 6-8 ppm FC to get the same kill rate, which most people arent maintaining.
The practical threshold where I start telling homeowners they have a problem is around 80-90. Above that and youre fighting an uphill battle keeping the pool safe. Only real fix is a partial or full drain since theres nothing you can add to reduce CYA.
The practical threshold where I start telling homeowners they have a problem is around 80-90. Above that and youre fighting an uphill battle keeping the pool safe. Only real fix is a partial or full drain since theres nothing you can add to reduce CYA.
one thing I want to add is that the drain and refill approach for high CYA isnt always practical if youre somewhere with water restrictions. we had to deal with this last summer and ended up doing partial drain and refills over like 3 weeks to get it down gradually. Drained about a third each time and refilled. took a while but it worked and we didnt waste as much water.
also worth noting that if you use stabilized chlorine tabs as your primary sanitizer your CYA is going to keep climbing no matter what. thats just how trichlor works, every tablet adds more CYA. switching to liquid chlorine or cal-hypo for daily sanitizing and only using tabs when you need the convenience is how I keep mine in check now
also worth noting that if you use stabilized chlorine tabs as your primary sanitizer your CYA is going to keep climbing no matter what. thats just how trichlor works, every tablet adds more CYA. switching to liquid chlorine or cal-hypo for daily sanitizing and only using tabs when you need the convenience is how I keep mine in check now
coming at this from the hot tub side - CYA matters there too but the numbers are different. for hot tubs the recommended range is lower, more like 30-50 ppm, because the water volume is small and temps are high which already stresses the chlorine. going above 50 in a hot tub is where I have personally noticed my sanitizer really struggling to keep up.
the drain and refill thing nroberts mentioned is kind of just the reality of it. there is no chemical shortcut to bring CYA down, dilution is the only way. for a hot tub at least draining and refilling is manageable since you are dealing with maybe 350-400 gallons, not 20,000.
the drain and refill thing nroberts mentioned is kind of just the reality of it. there is no chemical shortcut to bring CYA down, dilution is the only way. for a hot tub at least draining and refilling is manageable since you are dealing with maybe 350-400 gallons, not 20,000.