Hot tub start-up chemicals
Quick answer
On a fresh fill, add chemicals in this order: total alkalinity to 80 to 120 ppm, then pH to 7.2 to 7.8, then calcium hardness toward 150 to 250 ppm if the water is soft, then your sanitizer (chlorine 3 to 5 ppm or bromine 4 to 6 ppm), and finally shock. Order matters: alkalinity buffers pH, so setting it first keeps everything else from drifting.
A new fill is a blank slate, and getting the sequence right the first time is far easier than chasing a bounced pH later. The whole job is five steps and one round of shock.
What to have on hand
- Alkalinity increaser (sodium bicarbonate) to set the buffer.
- pH increaser and decreaser (soda ash and dry acid) to fine-tune from there.
- Calcium hardness increaser for soft fill water.
- Sanitizer: chlorine granules (dichlor) or bromine, depending on your choice below.
- Shock to oxidize the first round of contaminants, and test strips to read each step.
A start-up kit bundles most of these for a fresh fill, which is the simplest way to begin.
The order to add them
- Fill and circulate. Fill through a hose pre-filter to cut metals and hardness, switch on, and let the water warm and move before you test.
- Set total alkalinity first. Aim for 80 to 120 ppm. Alkalinity buffers pH, so locking it in first stops pH bouncing as you adjust everything else.
- Bring pH into 7.2 to 7.8. With alkalinity set, pH usually needs only a small nudge.
- Check calcium hardness. Soft fill water (below about 150 ppm) foams and can corrode, so raise it toward 150 to 250 ppm. See calcium hardness.
- Add sanitizer, then shock. Bring chlorine to 3 to 5 ppm or bromine to 4 to 6 ppm, then shock to clear the first contaminants. The dosing calculator sizes the alkalinity, pH, sanitizer, and shock steps for your gallons (dose the calcium increaser by its label).
Add in small steps with the pump running, wait, then retest before adding more. Never mix chemicals together, and always follow your product label, which wins over any calculator.
Chlorine or bromine to start?
Both sanitize well. Bromine is more stable at hot tub temperatures and gentler on skin, which suits most spas, while chlorine (dichlor) is cheaper and acts faster. If you are undecided, the chlorine vs bromine guide lays out the trade-offs. A bromine start also wants a one-time sodium bromide reserve, which the product label explains.
What helps
A spa start-up kit gathers the balancers, sanitizer, and shock you need for a clean first fill.
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Common questions
What order do I add hot tub start-up chemicals?
Total alkalinity first, then pH, then calcium hardness, then sanitizer, then shock. Alkalinity is the buffer that steadies pH, so setting it before everything else keeps the rest of the readings from drifting while you work.
How long before I can use a fresh fill?
Once alkalinity, pH, and sanitizer are in range and any shock has worked in (chlorine back down near 5 ppm, or a non-chlorine shock after about 15 minutes), it is ready. Re-test before the first soak to confirm the numbers held.
Do I need calcium increaser on every fill?
Only if your fill water is soft. Test calcium hardness first; if it is already in the 150 to 250 ppm range you can skip it. Soft water below that foams and can etch surfaces and corrode heaters, so it is worth raising.