Bugs in a Salt Water Pool: What They Are and Why They Stay

Salt does not keep bugs out of a pool. Most of the insects you find in a salt pool flew in overnight, and most will be gone after a skim. The ones that stay and breed, usually water boatmen and backswimmers, are telling you something: there is food in the water, and that food is algae.

A salt pool is a chlorine pool. The cell makes the same hypochlorous acid as bleach, at a salt level of about 3,200 ppm, roughly a tenth of ocean water. That is not salty enough to bother a bug that lives in ponds. If you are new to the equipment side, our salt water pools hub covers the basics, and this page sticks to what is swimming, floating or crawling in yours.

What is that bug?

Water boatmen

Water boatmen suck juices from algae, other plants, and detritus, according to the Missouri Department of Conservation, and they are among the few water bugs that do not bite people. The LSU AgCenter is blunter about pools: the boatman feeds on algae growing in the pool, particularly in the traps, filters and drains. One or two after a warm night is normal. A population that is still there a week later means they are eating.

Backswimmers

Backswimmers swim belly up and hunt. They prey on other aquatic insects and even small fish and tadpoles and can deliver a painful bite if you grab one. LSU describes the bite as a nasty, stinging sensation and notes that backswimmers eat water boatmen. So if you have backswimmers, you almost certainly had boatmen first.

Springtails

Springtails are about 1/16 inch long, wingless, and do not bite humans or pets or spread disease. The University of California IPM program says the ones in a pool will be removed by normal pool filtering or can be manually removed using a pool skimmer. They come from moisture and organic matter nearby, so wet mulch beds against the deck keep supplying them. Our guide to plants around a saltwater pool covers what to plant and where.

Mosquito and midge larvae

The mosquito risk is less the pool than the water sitting on or around it. San Diego County’s vector control program warns that pool covers can collect standing water from rain and irrigation, and that larvae can live in as little as 1/4” of water. A neglected green pool is worse: the county says mosquitoes that can carry West Nile virus like to use them, and its prevention advice starts with keeping filtration and sanitizer running. Pump the puddle off a winter cover.

Red worms on the pool floor are usually midge larvae. The Missouri Department of Conservation says some species are bright red from the hemoglobin and are called bloodworms, and that midges in this family do not bite people at all. They normally live on the bottoms of ponds and lakes, so a pool full of them has probably been sitting still for a while.

Beetles and other drowned bugs

Most dead bugs in the skimmer basket are not pool bugs at all. Both boatmen and backswimmers are attracted at night to artificial lights and land in pools after a night’s flying. A drowned bug that flew in tells you nothing about your chemistry.

Why the bugs stay: the algae chain

This is the part most bug advice skips. The chain runs like this:

1. Algae grows, often where you cannot see it yet: in the filter, behind steps, in the skimmer throat.
2. Water boatmen move in to eat it.
3. Backswimmers move in to eat the boatmen.

So killing the bugs one at a time treats the symptom. LSU’s own first step is chlorination: shock the pool, then scrub off the algae, and it states the logic plainly: with no algae in the pool, the bugs cannot survive there.

In a salt pool, algae almost always means free chlorine fell below what your cyanuric acid level needs. The floor is about 5% of your CYA, so at 70 ppm CYA you need about 3.5 ppm free chlorine as a minimum. The CYA and chlorine chart has the full table. A reading of 2 ppm can look fine on a strip and still be too low for the stabilizer you are carrying. If the walls feel slippery or the water is dull, go to algae in a salt water pool and deal with that first. The bugs follow.

What actually works

• Test free chlorine and CYA yourself. Hold FC at or above the CYA floor. If you need to push it up fast, see how to shock a salt water pool.
• Run the pump long enough. The cell only makes chlorine while water is flowing through it. See how long a salt generator takes to make chlorine and our guide on how to operate a salt water pool for run times.
• Brush and skim. Brush the walls, steps and corners where algae starts. A salt water pool cleaner handles the floor, but it will not scrub behind a ladder.
• Clean the filter. LSU specifically names traps, filters and drains as where boatmen feed.
• Change the lights. The University of New Hampshire Extension suggests you choose yellow light for your outdoor fixtures, use motion sensors, and leave outdoor lights off when you do not need them. Fewer bugs fly in.
• Drain the cover. Any standing water on a cover or in a closed pool is a mosquito nursery.

The dish soap trick

You will see advice to squirt dish soap on the surface. The mechanism is real. The University of Georgia Extension explains that soap disrupts the surface tension of water, which lets water into an insect’s breathing openings, so the bugs sink and drown.

The problem is that you are adding detergent to water people swim in. Swim University traces pool foam to exactly this kind of residue, and notes that even the residue left behind by your shampoo and conditioner can build up into a foam problem. It kills the boatmen you can see and does nothing about the algae that brought them. None of the extension sources we read recommends putting soap in a pool. LSU’s version of the trick is to skim the bugs out and drop them in a bucket of water and oil, which keeps the oil out of your pool.

Where to go next