As with most natural products, spa water has a shelf life. Most manufacturers agree three to four months is the recommended refill frequency or hot water cycle for a spa used on a regular basis. Periodically refilling your spa will ensure your water treatment chemicals work as efficiently and economically as possible.
A good rule of thumb to determine if your spa is ready for new water is to use this simple method: divide the spa gallonage by three. Then divide this result by the average number of bathers per day. The final results are the estimated number of days between water changes for a properly maintained hot tub. For example, a 600-gallon spa divided by three equals 200. If the spa averages two users a day, 200/2 = 100 days between refills.
Anytime you plan to change out your spa water is also a good time to purge the plumbing. Over time, water contaminants — body oil, lotion, deodorant, etc. — build up a film (biofilm) in the hot tub pipes, even if you maintain near perfect water chemistry. Several chemical manufacturers now offer purge/pipe cleaning products that should be used right before draining your hot tub to adequately clean all the nooks and crannies of your hot tub that you can’t otherwise get to.
While instructions vary, in most cases, these products are added to the water 12-24 hours before draining. You will need to periodically run the jets, often in five- to 20-minute intervals (the product will often foam, so short intervals are ideal), over the allotted time period. After the 12-24 hours, drain the hot tub, rinsing as the pipes clean out. You’ll most likely see black flecks and other gunk floating in the water. As you’re draining the hot tub, wipe this debris away with a soft cloth. Once the hot tub is empty and you’ve wiped it clean you’re ready to refill it with fresh water.
A purge is like doing a factory reset on your hot tub, getting everything back to how it was the first time you ever turned your spa on. Hot tubs care is remarkably manageable with proper chemical additions, routing testing, regularly draining and refilling and the assistance of a reputable spa retailer.