How to Clean a Hot Tub That Has Been Sitting
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It doesn't take long for spa water to go south when the hot tub has been sitting for days or weeks without being filtered or sanitized. How long? In moderate temperatures, spa water can stay fresh for up to two weeks, if covered tightly.
Spa water that sits longer than a week or two will begin to grow algae and bacteria, even without light and under a dark spa cover. Spas that sit untended will begin to grow biofilm or bacterial colonies. It's the kind of scum you see in a toilet that hasn't been used or cleaned in a while (sorry for that analogy!).
For spas and hot tubs that have been sitting unused and unmaintained for a period longer than a few weeks, here's the process to bring it back online.
TEST THE FILTER SYSTEM
Before you do a lot of work cleaning the hot tub, make sure that the spa pump and filter are operational. Add water if needed to bring the level up to mid-skimmer, covering the spa filter, which may need to be replaced with a new filter cartridge.
Turn on power at the circuit breaker, then open up the spa cabinet to find the spa equipment. Reset any popped GFCI outlets, and power up the spa pack. Check that all valves are open (before and after the pump), and take a good look for any leaking water under the spa.
Using the spa side control, run the spa pump on low speed and high speed briefly, which will help dislodge gunk in the pipes. Some spas have two pumps: a circulation pump and a jet pump. Test them both to be sure that they will be operational after you drain and clean the hot tub.
DRAIN & CLEAN
Draining the water is the best way to clean a hot tub that has been sitting for awhile. If your water is in fair condition, looking hazy but without visible algae or biofilm growth, skip ahead to the next step and purge the plumbing.
To drain a spa or hot tub, look for the drainage port or hose. Some spas have a small access port at the base of the cabinet to drain water. If not, you will usually find a short hose or a hose connection at the lowest point of the spa. Pull out the hose or connect a hose, and let the water drain by gravity. You can also use a submersible pump to drain a spa. Be sure that the power to the spa is OFF before draining.
As the spa is draining, if the water condition is really bad, use a garden hose to spray off the spa surfaces. You can also spray water into the skimmer or directly into the spa jets to help loosen slimy gunk. Just be careful not to spray the spa pack or spa equipment (pump, filter, heater).
REFILL & PURGE
Now that you've removed the funky, gunky water from the hot tub (or if you want to clean a hot tub without draining), the next step is to purge the spa. In this step, you'll add a specialized chemical to remove the slimy biofilm lining the inside of the pipes, which makes its home in the various nooks and crannies in the spa's air and water plumbing.
We recommend using products like Leisure Time's Jet Clean to remove biofilm, mineral deposits, oils and other organic contaminants from the spa plumbing. Follow label directions, adding it to the spa with the pump system running. In a very short time, you will notice the funk and gunk rising to the surface as a brown foam. Turn on the jet pump and blower to help dislodge any remaining bacterial colonies.
DRAIN & REFILL
Drain the spa once more, using a hose or rag to remove the scum around the top of the spa, cleaning as the water level drops. When the tub is completely empty, use sponges or a wet/dry vac to suck up the last bits of dirty water. This will help get rid of all the bacteria and other gunk that the purge removed from the spa lines, ensuring that you'll have a fresh start with nice, clean water in your hot tub!
One more time to the well! Refill your spa with fresh water. When full, test the water chemistry and add adjustment chemicals if needed to balance the pH, alkalinity and calcium hardness. Add a bromine booster (if you use bromine tabs), then shock the hot tub with 1-3 tablespoons of spa shock, following label instructions.
A new spa filter may also be in order to keep the hot tub water clean and clear. Replace your spa filters every 18 months, or every 12 cleanings, whichever comes first.