Emily_Ross
New member
The pool was clear yesterday, but today it’s cloudy. Levels look fine. What could cause sudden cloudiness overnight?
Crystal clear one day, cloudy the next?
- Thread starter Emily_Ross
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William Walker
Member
Hey Emily, I've had that happen before, and it could be a couple of things. Even if your levels look good, sometimes it’s the filtration system not running long enough to catch everything. If the filter wasn’t running overnight, fine particles might have floated back into the pool. Another thing could be a quick shift in temperature, which can cause some chemical imbalances to create cloudiness even if everything else looks fine. It’s always good to double-check those filters!
Mark Davis
Member
Sudden cloudiness overnight usually means something changed fast in your water. Even if your chlorine, pH, and alkalinity looked fine yesterday, there could’ve been a spike in contaminants like pollen, dirt, or sunscreen from swimmers. Sometimes a small rainstorm or a windy night blows in fine debris that your filter can't grab right away. I’d check your filter first if it’s dirty or clogged, it won’t clear that stuff out fast enough. I also run a clarifier when this happens, just to help the filter trap those tiny particles. And don’t forget, chlorine gets used up fighting off invisible stuff like sweat or organic matter even if no one swam, so I sometimes give it a light shock just to be safe.
Ryan Brooks
Member
This happened to me last month. The pool looked perfect one day, then cloudy the next morning. Turned out my filter wasn’t running long enough overnight when pollen was falling heavy. Even though my chemical levels tested okay, the fine particles built up faster than the filter could clear them. I ran the pump longer and added a clarifier, and it cleared up in a day. Sometimes it’s also a pH swing from temperature changes overnight if the pH shifts too much, it throws off how well chlorine works, even if the numbers seem close to normal. Keeping an eye on run time and fine-tuning your schedule during weather changes can help prevent these surprises.
Kevin Marsh
Member
Had something like this happen after a super clear day, woke up to murky water and couldn’t figure it out at first. My readings looked decent, too. What I found later was that my skimmer basket had clogged up with leaves overnight, so the circulation stalled.
It’s one of those little things that’s easy to miss, especially if the surface looks fine. Water was moving, just not enough. Once I cleared it out and backwashed the filter for good measure, it started clearing within a few hours.
Might not be your issue exactly, but maybe worth checking if something slowed the flow down without being super obvious.
It’s one of those little things that’s easy to miss, especially if the surface looks fine. Water was moving, just not enough. Once I cleared it out and backwashed the filter for good measure, it started clearing within a few hours.
Might not be your issue exactly, but maybe worth checking if something slowed the flow down without being super obvious.
Michael Young
Member
I’ve had the same issue. It turned out my filter wasn’t running overnight, and the fine particles floated back in. After checking the filter and running the pump longer, the water cleared up. Maybe check the filter again and ensure the pump runs continuously during weather changes!
Mason Blake
Member
I’ve seen that happen when calcium levels get out of balance. The water looks fine until conditions shift a bit overnight, then tiny scale particles form and make it hazy. A quick calcium hardness test and adjustment solved it for me. Worth checking if the usual tests all look good.
Liam Brooks
Member
I’ve run into this a few times and what finally clicked for me was that “levels look fine” doesn’t always mean the water is actually stable.
One thing I don’t see mentioned yet is overnight sanitizer demand combined with no UV. At night, chlorine isn’t getting burned off by the sun, so if there’s a lot of invisible organics in the water, pollen, dust, sunscreen residue, whatever, the chlorine works on that instead. By morning you can have higher combined chlorine and slightly lower effectiveness, which shows up as cloudiness even though the numbers don’t look scary. By midday, sunlight helps burn that off and the water sharpens up again.
Another sneaky cause I’ve seen is borderline calcium balance. When water cools overnight, calcium can fall out of balance just enough to create a light haze, then redissolve once temps rise. It doesn’t look like scale, just dull water. I noticed this when my saturation index was right on the edge and filter pressure barely changed, maybe 1 psi, but clarity did.
When this happens to me now, I check trends instead of assuming it’s random. Is pH drifting day to day, is CC creeping up, is calcium riding the edge. Sudden cloudiness overnight is usually the water telling you something’s just barely out of line, not that everything broke at once.
One thing I don’t see mentioned yet is overnight sanitizer demand combined with no UV. At night, chlorine isn’t getting burned off by the sun, so if there’s a lot of invisible organics in the water, pollen, dust, sunscreen residue, whatever, the chlorine works on that instead. By morning you can have higher combined chlorine and slightly lower effectiveness, which shows up as cloudiness even though the numbers don’t look scary. By midday, sunlight helps burn that off and the water sharpens up again.
Another sneaky cause I’ve seen is borderline calcium balance. When water cools overnight, calcium can fall out of balance just enough to create a light haze, then redissolve once temps rise. It doesn’t look like scale, just dull water. I noticed this when my saturation index was right on the edge and filter pressure barely changed, maybe 1 psi, but clarity did.
When this happens to me now, I check trends instead of assuming it’s random. Is pH drifting day to day, is CC creeping up, is calcium riding the edge. Sudden cloudiness overnight is usually the water telling you something’s just barely out of line, not that everything broke at once.