Under most real-world conditions, the water in a swim spa tub, without added disinfectant, typically only maintains a safe usage period of 1–3 days. After this time, bacteria, fungi, algae, and other microorganisms will begin to multiply rapidly, leading to irreversible water quality deterioration.

Even after you empty the bathtub, bacteria and sticky dirt may remain on the interior surfaces. If you don't flush before draining, these bacteria will continue to adhere to the surfaces and may even re-enter the circulation system during the next refill.

Generally, at least 24 hours should be waited after a chlorine shock, and testing should be conducted to ensure that the free chlorine concentration has returned to a safe range of 1–3 ppm (parts per million) before entering the Swim spa tub.

Chlorine is the most common disinfectant used in pools and spas, but its healthiness in swim spa tubs depends on how it is used. • Strong bactericidal power: Effectively kills most bacteria, viruses, and algae; • Low cost: Economical, practical, and easy to purchase.

Turbidity in the swim spa tub is one of the most direct signs. Aggregation of bacteria and microorganisms, and redispersement of suspended matter, make the water appear unclear. Especially noteworthy is persistent turbidity rather than turbidity caused by short-term agitation.

In fact, bacterial growth is one of the most serious consequences of not changing the water for a long time. The temperature in a swim spa tub is usually between 30–38°C, a temperature range that is the ideal growth environment for most bacteria.