Woke up to milky white pool water overnight what could cause such a sudden change?

[Freddie]

Last night the pool looked perfectly clear but this morning it’s completely milky white. Not cloudy, not hazy actually white like diluted milk. Pump was running all night and nothing unusual happened. I checked chlorine and it was a bit high but not crazy. Never seen water change this fast. What could cause such an overnight disaster?

 

[Zephyr]

Last night the pool looked perfectly clear but this morning it’s completely milky white. Not cloudy, not hazy actually white like diluted milk. Pump was running all night and nothing unusual happened. I checked chlorine and it was a bit high but not crazy. Never seen water change this fast. What could cause such an overnight disaster?

I had that happen when my filter cracked internally. It dumped a bunch of DE back into the pool without me noticing. Look at your returns if they puff out white clouds when you start the pump that might be it.

 

[Manikshaw]

Last night the pool looked perfectly clear but this morning it’s completely milky white. Not cloudy, not hazy actually white like diluted milk. Pump was running all night and nothing unusual happened. I checked chlorine and it was a bit high but not crazy. Never seen water change this fast. What could cause such an overnight disaster?

Another possibility is calcium reacting with something you added. If your CH is high and you shocked the pool at night sometimes it precipitates into the water and turns it milky. Test your calcium level just to rule that out.

 

[syedsam]

Last night the pool looked perfectly clear but this morning it’s completely milky white. Not cloudy, not hazy actually white like diluted milk. Pump was running all night and nothing unusual happened. I checked chlorine and it was a bit high but not crazy. Never seen water change this fast. What could cause such an overnight disaster?

Could also be an algae die-off if you recently treated it. When algae dies really fast especially green algae, it can turn the whole pool opaque until the filter catches up. Check if the bottom is slippery that’s usually a clue.

 

[Freddie]

Thanks for the fast responses. I checked the returns and they did spit out a little white dust when I restarted the pump so the DE filter might be the culprit. I’ll open it up later today and check for cracks.

 

[Matthew Collins]

If you saw white dust puff out of the returns when the pump restarted, that definitely points toward the filter, but one other thing that can cause that milky look overnight is calcium falling out of solution. I ran into that once after a hot stretch where the pH drifted up without me noticing.

The pool looked crystal clear in the evening, then by morning it had that exact diluted milk look you’re describing. My calcium hardness was already on the higher side and the pH had crept up close to 8.0, so the saturation index basically tipped and the calcium started precipitating into the water. It turns the whole pool white even though nothing “dirty” actually got in.

What tipped me off was the filter pressure rising pretty quickly once the pump kept running. Mine climbed about 4 to 5 psi as the filter started catching those tiny calcium particles. After bringing the pH back down into the mid 7s and letting the system run for a day, the water cleared again.

Since you’re seeing powder from the returns though, checking the DE grids or manifold is still a really good move. When those get a small tear it can dump DE back into the pool and the water looks almost identical to a calcium cloud.