Swamp cooler smells musty or fishy: what causes it and what the fix costs in Reno

A swamp cooler that smells musty, fishy, or like a pond has water sitting where it should be moving: a stagnant pan, algae on the pads, or aspen pads that are past their life and holding grime. The fix is a pan clean and fresh pads, $80 to $250 on top of a $150 to $350 service call, or included in a $120 to $250 spring start-up if the smell shows up in May. The thing that keeps it from coming back is a working bleed-off line, and that gets set on the same visit.

Check this first (five minutes)

Look in the pan. Pull a side panel. A film on the water, green or brown growth on the pan walls, or a layer of sludge at the bottom is the source. A pan that smells with the pump off is the whole answer.
Look at the pads. Aspen pads that are dark, slimy, or matted are done. Rigid media with green streaks has algae; with a white crust it is scale, which does not smell but does trap grime.
Check the bleed-off. If the cooler has a bleed-off line, water should be trickling out of it while the pump runs. A dry bleed-off means the pan water is just recirculating and concentrating.
Run pump-only for five minutes, then the blower. If the smell fades after the pads wet through, it is a dried-pad smell and pump-only before blower will manage it; if it stays, the pan needs cleaning.

What is usually wrong

Symptom detail	Likely cause	Fix and cost
Smell in May at start-up	Pads left in over winter, pan never dried	Pan clean + new pads, with the start-up
Fishy smell all summer	Stagnant pan, no bleed-off running	Pan clean, bleed-off set, $150 to $350 call
Musty burst when it first turns on	Pads dried between cycles	Pump-only before blower; new pads if bad
Green pads, slime on the pan walls	Algae	Pan clean, new aspen $80 to $200, or media treatment
Smell plus weak airflow	Matted pads	New pads, $80 to $200 aspen or $300 to $700 media
Burning smell, not musty	Motor or belt, different problem	See the motor, bearings, and belt page

Every number is from the pricing page. A burning smell is not this page; that is the squeal and rattle page or the motor page.

Why Reno coolers smell

Two things about this valley make the smell more common than it should be. First, the diurnal swing: Reno’s July normal high is 93.9 and its normal low is 60.4, so a lot of households shut the cooler off at night and turn it on at noon. Pads that dry out every night and re-wet every noon grow things, and the noon start blows them into the house. Pump-only for a few minutes before the blower is the habit that fixes it.

Second, the winter. A cooler that is not drained and dried in October sits with a wet pan and damp pads through 111.6 freezing nights, and whatever survives the cold wakes up in April. The fall winterization pulls the aspen pads and dries the pan for exactly this reason, and the start-up in spring cleans whatever is left.

Scale plays a supporting role. Reno’s river water is soft on average, but TMWA’s published samples run as high as 13.9 grains per gallon in some areas and quarters, and a crust on the pads traps grime and holds moisture. A bleed-off line that dumps a small stream of pan water continuously keeps the concentration down and the pan moving, and the pump and float page explains how it is set.

What the fix includes

The pan gets drained, scraped, and washed out, the pump screen gets cleared, the aspen pads get replaced or the rigid media gets rinsed and treated, the bleed-off or purge gets set, and the distribution tubes get cleared so the pads wet evenly. Then pump-only, then the blower, and the smell should be gone by the time the ladder comes down. On a cooler that has been smelling for a season, the tech also checks the pan for rust under the sludge, because standing water is how galvanized pans start to go; the installation page covers what happens if it has.

What to expect on the call

Say when the smell started and whether the cooler was drained last fall. Send a photo of the pan with the panel off and one of the pads. The tech arrives with aspen pads for the common sizes, cleans the pan on the visit, and sets the bleed-off so the next call is a start-up, not a smell.

Frequently Asked Questions

Why does my swamp cooler smell like a swamp?

Stagnant water in the pan, algae or slime on the pads, or aspen pads past their life. A cooler that sat through a warm week with the pump off, or pads that were left in over the winter, grows a smell fast. A pan clean and fresh pads fix it, and a working bleed-off keeps it from coming back.

How much does it cost to fix a smelly swamp cooler in Reno?

A pan cleaning and a new set of aspen pads run $80 to $250 on top of the $150 to $350 service call, or ride on a $120 to $250 spring start-up if the smell shows up in May. Rigid media pads that have gone slimy get rinsed and treated; replacement is $300 to $700 if they are past saving.

Is the smell dangerous?

It is unpleasant more than dangerous, but a pan growing slime is a pan pushing that air into the house, and anyone with allergies or asthma will notice. Fix it rather than living with it, and keep the pan draining and the pads fresh so it does not return.

Why does it smell worse when I first turn it on?

Because the pads dried out between cycles and whatever grew on them is being wetted and blown into the house at once. Running pump-only for a few minutes before the blower wets the pads evenly and flushes the worst of it out the bleed-off instead of into the hall.