Pool turned bright green overnight after heavy rain
- Thread starter Manikshaw
- Start date
John Faulkner
Member
Test your water first rain usually lowers chlorine and alkalinity. Balance those and you’ll clear it faster.
Brandon Hayes
Member
One thing I’d check, too, is how much debris or fine dirt might have washed in with that rain. Even if you don’t see leaves floating, runoff can sneak a lot of nutrients into the water that feed algae. A good vacuum and brushing right after shocking makes a big difference; otherwise, the algae just keeps grabbing hold. Keeping the skimmer baskets clear helps circulation too, especially after a big storm.
Liam Brooks
Member
Yeah, rain can flip things fast, but it’s usually not just dilution. I’ve noticed after really heavy rain the bigger issue is what the water brings with it. All that runoff dumps fine dust, pollen, and whatever was sitting on the deck or lawn straight into the pool. Even if free chlorine shows up on a test, it can get overwhelmed trying to chew through all that new gunk at once.
One time this happened to me, my chlorine wasn’t actually zero, but combined chlorine shot up and the water temp stayed warm overnight. That combo is perfect for algae to explode. Filter pressure crept up a few psi by morning too, which told me the filter was catching a ton of junk. Brushing the walls and especially the floor before shocking made a big difference, otherwise the algae just stayed glued on.
I’d also check where your water level ended up after the rain. If it climbed high enough to dilute stabilizer, chlorine can burn off way faster the next day in the sun. Rain doesn’t cause green water by itself, it just stacks the deck against you all at once. Anyone else notice their filter clog way faster after storms?
One time this happened to me, my chlorine wasn’t actually zero, but combined chlorine shot up and the water temp stayed warm overnight. That combo is perfect for algae to explode. Filter pressure crept up a few psi by morning too, which told me the filter was catching a ton of junk. Brushing the walls and especially the floor before shocking made a big difference, otherwise the algae just stayed glued on.
I’d also check where your water level ended up after the rain. If it climbed high enough to dilute stabilizer, chlorine can burn off way faster the next day in the sun. Rain doesn’t cause green water by itself, it just stacks the deck against you all at once. Anyone else notice their filter clog way faster after storms?
Sean Whitaker
Member
I had almost the exact thing happen a couple summers ago. Went to bed with the pool looking perfect and the next morning it was bright green. At first I blamed the rain for “turning it green,” but what really happened was the rain basically reset the chemistry and dumped a bunch of new stuff into the water at the same time.
Heavy rain can dilute chlorine a bit, but the bigger issue is usually what washes in. Pollen, soil dust, fertilizer residue, even tiny organic particles from the yard can end up in the pool overnight. All that becomes food for algae. If chlorine was already a little on the low side, that sudden nutrient load can let algae take off fast.
One thing I noticed when it happened to me was the filter pressure climbing a few psi the next day. The filter was catching tons of fine debris the storm had pushed into the pool. After brushing the walls and floor and letting the pump run continuously, the water started improving once the sanitizer caught up.
So yeah, rain itself doesn’t create algae, but it can dilute chemicals, add contaminants, and push the pool just far enough out of balance that algae shows up quickly. Storms are one of those times where testing and brushing right away really helps get ahead of it.
Heavy rain can dilute chlorine a bit, but the bigger issue is usually what washes in. Pollen, soil dust, fertilizer residue, even tiny organic particles from the yard can end up in the pool overnight. All that becomes food for algae. If chlorine was already a little on the low side, that sudden nutrient load can let algae take off fast.
One thing I noticed when it happened to me was the filter pressure climbing a few psi the next day. The filter was catching tons of fine debris the storm had pushed into the pool. After brushing the walls and floor and letting the pump run continuously, the water started improving once the sanitizer caught up.
So yeah, rain itself doesn’t create algae, but it can dilute chemicals, add contaminants, and push the pool just far enough out of balance that algae shows up quickly. Storms are one of those times where testing and brushing right away really helps get ahead of it.