Keeping a pool clean with Ohio trees and pollen

Pools in Northeast Ohio are rarely far from trees. Wooded lots, mature street maples and the tree lines along the back of many subdivisions all drop something on the water for most of the swim season. It helps to think of it as a calendar.

• March to May: tree pollen. Ohio health departments put most tree pollen between March and May, with oak, birch and maple peaking around April. Pools opened in May often meet the tail end of it.
• Spring: maple seeds and oak flowers. The winged seeds and the stringy oak catkins float, clog skimmer baskets and stain if left to sit.
• Late May into June: cottonwood fluff. OSU Extension says cottonwood seeds are usually ready to shed by the end of May and can keep releasing into June and early July, typically for two to three weeks.
• May to June: grass pollen, which takes over from tree pollen in early summer.
• Summer: sap, aphid honeydew and the odd twig after a thunderstorm.
• October: leaves. The Ohio Department of Natural Resources expects fall color to peak in mid to late October across northern Ohio, and the leaves come down right after.

Pollen grains are small and light, so they float. They collect as a yellow or greenish film on the surface, pile up in corners where the water circulates least and sink as a fine dust that looks a lot like mustard algae. It is not algae, but it does feed algae and it uses up chlorine as it breaks down.

The fix has three parts. Skim it off the surface before it sinks, ideally every day during heavy pollen weeks. Run the pump longer, and at a higher speed for part of the day, so the skimmers pull the surface film in. And keep chlorine steady, because a pool that is short of chlorine during pollen season turns from dull to green quickly.

Filtration matters here more than anywhere. Pollen is fine enough that a coarse filter lets some of it back into the pool. That is one reason every Ohio State Pools package comes with a Pentair DE filter, which Pentair rates at under 5 microns. Expect to clean the filter more often during pollen season. The pressure gauge tells you when.

Maple seeds and oak catkins are big enough for the skimmer basket to catch, which means the basket fills fast. Check and empty skimmer baskets daily in spring, and the pump basket every few days. A full skimmer basket starves the pump of water, which is hard on the pump and stops skimming altogether.

Cottonwood fluff is its own nuisance. It mats on the water surface and wraps around skimmer weirs. OSU Extension notes it can drift a long way on the wind, so you can get it even without a cottonwood on your lot. A leaf net on a pole, used daily, and a cover when nobody is swimming keep most of it out. Clean the skimmer weir door if it starts sticking.

Leaves are the heaviest debris load of the year, and they tend to arrive when the pool is still open or just about to close. In a big October drop, a pool under mature oaks or maples can collect more leaves in a day than any cleaner can handle.

Stop them before they sink. Wet leaves on the bottom release tannins that stain a light pool finish tea-colored and feed algae as they rot. A leaf net stretched over the pool during the peak weeks, or an automatic cover left closed when you are not swimming, is the most effective tool you have. Skim what gets through daily and use a leaf rake with a deep bag for the heavy days.

Timing your closing helps too. Some owners close in September, before the worst of the leaf drop. If you like to swim into October with a heater, plan on netting the pool or keeping the cover on between swims. At closing, a winter safety cover keeps the leaves out until spring.

A few inexpensive tools save a lot of time. A deep-bag leaf rake on a telescoping pole moves far more debris per pass than a flat skimmer net. Skimmer basket liners, sometimes called skimmer socks, catch fine pollen and cottonwood fluff before it reaches the pump and filter, and you can shake them out in seconds. A leaf canister on the suction line, if your cleaner uses one, keeps leaves out of the pump basket.

A spare skimmer basket helps too. Swap in the clean one and let the full one dry, which makes emptying it much easier. And keep the pump basket lid O-ring clean and lubricated, because you will be opening it more often than usual in spring and fall.

Midsummer is quieter for debris, but not clean. Some trees drip sap, and in some years aphids feeding on shade trees rain sticky honeydew onto everything below them. OSU Extension has written about Ohio summers bad enough to be called a "Year of the Aphid," with honeydew coating cars, decks and patio furniture. On a pool it shows up as a sticky film at the waterline and a slick on the deck.

A pool-safe waterline cleaner and a soft brush take care of the tile line or the fiberglass edge. Hose the deck off before it bakes on. If one tree is the culprit every year, it is worth having an arborist look at it, or thinking about it when you plan any new planting.

For pollen, sand and fine debris, a robotic cleaner is excellent. It scrubs the floor and walls and catches fine material in its own filter, which takes load off the main filter. Rinse its basket after every run during pollen season.

For leaves, robots struggle. Their baskets hold a limited volume, and in a heavy drop they fill in the first hour. Pressure cleaners with big debris bags do better with leaves but use far more electricity. Either way, a cleaner is the second line of defense. Skimming and covers are the first. Our guide comparing robotic cleaners and built-in systems goes into this in more detail.

Organic debris, whether pollen, seeds or leaves, consumes chlorine as it breaks down. That means your usual chlorine dose may fall short during heavy weeks. Test more often, keep free chlorine at or above the level CDC recommends, at least 1 ppm, or 2 ppm if you use stabilized chlorine, and keep pH in range so the chlorine works. After a big storm or a heavy drop, shock the pool once the debris is out.

Do not leave debris in the water and try to chlorinate around it. Remove it first, then treat. Chlorine spent breaking down a pile of leaves is chlorine not protecting swimmers.

The easiest debris to deal with is debris that never reaches the pool. When we design a pool, we look at the trees around it: what species they are, which way the prevailing wind blows across the lot, and where the shade falls in the afternoon.

Some practical choices follow. Place the pool so the main skimmer sits downwind, where the wind pushes floating debris toward it. Keep the pool back from the drip line of big maples and oaks where you can. Choose low-litter plants for beds right beside the deck, and avoid anything that drops berries, sticky sap or lots of small flowers onto the water. And plan an automatic cover if you have heavy tree cover, because it pays for itself in time saved.

We show the pool, deck and planting in 3D on your lot before we dig, so you can see how close the trees really are. Taking out one messy tree before the pool goes in is much cheaper and easier than working around it after.

Some yards are simply a lot of work in May and October. If the debris weeks are more than you want to take on, our pool service covers weekly cleaning, skimming, water testing and chemical balancing, equipment checks, openings and closings. Many owners use it only through the heavy weeks and handle the easy midsummer stretch themselves.