Domakihub How to Shock a Hot Tub: Keep Your Water Safe and Clear
A step-by-step guide to shocking your spa with the right chemical at the right dose.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
Shocking a hot tub is one of the most important maintenance tasks you can do — it destroys the combined chloramines, bacteria, and organic waste that build up after every soak. The video above walks through the full process visually; the guide below gives you the exact steps and doses so you can do it confidently at home, in your holiday rental, or at your hotel property. Whether your tub sits on a rooftop in Athens or a terrace in Crete, the hot Greek summers mean water quality degrades faster than you might expect.
Why Hot Tub Water Needs Shocking
Regular sanitiser (chlorine or bromine) handles day-to-day bacteria, but over time it reacts with body oils, sunscreen, and sweat to form chloramines — the compounds that cause that sharp chemical smell and red eyes. Shocking the water with a high-dose oxidiser blasts those compounds apart and restores free sanitiser to active duty.
In Greece, UV radiation and warm ambient temperatures accelerate chemical consumption. Hot tubs used by guests in holiday rentals or hotels should be shocked after every heavy-use period, not just on a weekly schedule.
Chlorine Shock vs. Non-Chlorine Shock (MPS)
Chlorine-based shock (calcium hypochlorite or dichlor) is the stronger option — it kills bacteria, oxidises waste, and boosts sanitiser levels simultaneously. The downside is a mandatory 8–24 hour wait before the tub is safe to use again.
Non-chlorine shock (potassium monopersulphate, or MPS) oxidises organic waste quickly and lets you re-enter the water after just 15–30 minutes. It does not sanitise on its own, so it works best when your chlorine or bromine level is already in the correct range. For rental properties between guest stays, chlorine shock is the safer default.
How to Shock Your Hot Tub in 5 Steps
- 1
Test the water first
Use a reliable test strip or a liquid test kit to measure your current free chlorine, pH, and total alkalinity. Aim for pH 7.2–7.6 and total alkalinity 80–120 ppm before you add any shock. Out-of-range pH reduces the effectiveness of the shock chemical by up to 50%, so adjust first if needed.
- 2
Choose your shock and calculate the dose
For chlorine shock (dichlor or calcium hypochlorite), the typical dose is 30–50 g per 1,000 litres of water. Check the packaging for your exact product, as concentrations vary. For MPS non-chlorine shock, a standard dose is 35 g per 1,000 litres. Never mix different shock chemicals or add shock directly on top of existing sanitiser tablets.
- 3
Run the jets and remove the cover
Switch on the circulation pump and open the hot tub cover fully. Good water movement ensures the shock dissolves evenly and prevents concentrated patches from bleaching your shell or damaging the jets. Leave the cover off during the entire treatment to allow gases and byproducts to escape safely.
- 4
Add the shock to the water
Dissolve granular shock in a clean plastic bucket of warm water first — never add granules directly onto the surface in one spot. Pour the solution slowly around the perimeter of the tub with the jets running. Keep the pump circulating for at least 30 minutes after dosing. Wear gloves and eye protection when handling shock chemicals.
- 5
Wait, re-test, then re-cover
For chlorine shock, wait at least 8 hours (overnight is ideal) before testing again. For MPS, 15–30 minutes is sufficient. Re-test free chlorine (target 3–5 ppm for hot tubs), pH, and alkalinity before anyone enters the water. Once levels are within range, replace the cover to conserve heat and keep debris out.
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FAQ
- How often should I shock my hot tub?
- As a minimum, shock once a week for regular home use. Shock after every heavy-use session (more than 2–3 bathers), after a party, after someone has been ill in the water, or after a prolonged period of non-use. In Greek summers, weekly shocking is the absolute minimum — consider twice a week for holiday rentals with frequent guest turnover.
- Can I shock a hot tub with regular pool shock?
- Pool chlorine shock (calcium hypochlorite at 65–70%) can be used in a hot tub, but use it carefully and at lower doses because hot tubs hold far less water than pools. The better choice for most hot tub owners is dichlor (dichloroisocyanuric acid), which is pH-neutral and dissolves quickly in hot water. Always double-check that any product you use is rated for spas and hot tubs.
- My water is still cloudy after shocking — what went wrong?
- Cloudy water after shocking usually points to one of three things: the pH was too high before shocking (reducing effectiveness), the water had very high organic load requiring a second dose, or your filter cartridges are clogged and need cleaning. Remove and rinse the filter, re-test your chemistry, and apply a second shock dose if needed. If cloudiness persists after 24 hours, a full drain and refill may be the fastest fix.