You just finished draining, scrubbing, and refilling your Master Spas hot tub after a long winter — and now you're staring at a tub full of fresh, cold tap water wondering what goes in first. Get the order wrong and you'll chase cloudy water, burning eyes, and itchy skin for weeks. Get it right, and your spa will run crystal-clear all the way into summer.
Spring hot tub water chemistry isn't complicated, but it is sequential. Every chemical you add either helps or fights the one you added before it. Miss the order and you'll waste product, damage your heater, or keep the sanitizer from doing its job. This guide walks you through exactly what to test, what to add, and in what order — with the specific target ranges Master Spas recommends so you're not guessing.
Whether you're opening a Twilight Series, Legend Series, Healthy Living, or swim spa, the chemistry basics are the same. Let's get your water right the first time.
Why Spring Water Chemistry Is Different
Fresh fill water is a blank slate — and that's exactly the problem. Your tap water comes in with whatever your local supply throws at it: high alkalinity, low calcium, trace metals from old pipes, or just wildly unstable pH. Before your spa even heats up, you need to test that raw water and correct it before any sanitizer goes in.
This is the step most owners skip, and it's why their water turns green, cloudy, or foamy within a week of opening. A balanced spa starts with balanced fill water, not balanced hot tub water three days later.
Step 1: Test the Fresh Fill Water First
Before you turn on the heater, dip a test strip. You're looking for four numbers that set up everything else:
- pH: 7.2 – 7.8 (ideal 7.4 – 7.6)
- Total alkalinity: 80 – 120 ppm
- Calcium hardness: 150 – 250 ppm
- Free chlorine or bromine: 0 ppm at this stage (you'll add sanitizer last)
Cheap strips work, but dialed-in owners go with a full 6-in-1 strip that also reads stabilizer and hardness. Grab a pack of Aquachek Chlorine Test Strips (50-count) and keep them within arm's reach of the spa — you'll use them all season.
Step 2: Adjust Alkalinity Before Anything Else
Total alkalinity is the buffer that holds your pH steady. If you fix pH first while alkalinity is off, your pH will drift right back within hours. Always handle alkalinity before pH.
If your alkalinity reads below 80 ppm, add an alkalinity increaser (sodium bicarbonate). A 2-lb jug of HT pH/Alkalinity Increaser will bump both at once and is the simplest option for most owners. Add it with jets running, wait 15 – 20 minutes, and retest.
If alkalinity reads above 120 ppm, add a pH/alkalinity decreaser (sodium bisulfate). Go slow — a little goes a long way, and over-correcting creates a yo-yo effect.
Step 3: Dial in pH
Once alkalinity is in range, retest pH. If it's still below 7.2 after the alkalinity adjustment, a small additional dose of pH increaser will bring it up. If it's above 7.8, use pH decreaser.
Why this matters: sanitizer efficiency collapses outside the 7.2 – 7.8 window. At pH 8.0, chlorine is only about half as effective as it is at 7.4. You can dump in all the chlorine you want — if pH is off, your water will still go cloudy.
Step 4: Check Calcium Hardness
Calcium hardness prevents two bad outcomes. Too low, and the water pulls minerals out of your heater element and jet hardware. Too high, and you get scale buildup on your shell and plumbing.
Target: 150 – 250 ppm. Most municipal water in the U.S. falls in the 100 – 150 ppm range, so you'll probably need to add a calcium booster on a fresh fill. Well water owners usually have the opposite problem and need to soften.
Step 5: Shock, Then Sanitize
With your balance set, it's time to sanitize. Start with an oxidizing shock to burn off any contaminants introduced during the fill, then add your sanitizer.
For the shock, a non-chlorine oxidizer like HT Oxy Shock is gentler on your cover and bather skin than a chlorine shock, and it won't spike your chlorine level before you've set your baseline. Run jets for 15 minutes after adding.
Once the shock has circulated, add your primary sanitizer. Master Spas recommends sodium dichlor chlorine granules, which dissolve fast and don't over-stabilize the water. A 2-lb jar of HT Spa Chlorinating Granules will keep most 4 – 7 person tubs running for a couple of months. Aim for a free chlorine reading of 3 – 5 ppm on your test strip before the first soak.
• HT Spa Starter Kit — pH increaser, calcium booster, chlorine granules, shock, stain & scale, and test strips in one box
• HT pH/Alkalinity Increaser (2 lb) — your first line of defense on low-alkalinity fill water
• Aquachek Test Strips (50 ct) — test twice a week for the first month to lock in your baseline
Step 6: Heat, Circulate, and Retest in 24 Hours
Chemicals dissolve and react faster at temperature. Once your balance is set and sanitizer is in, close the cover and let the spa heat to 100°F+ with filter cycles running. After 24 hours, retest every parameter. You'll often see small shifts — top off whatever drifted, and that's your baseline.
From there, plan to test 2–3 times a week for the first month, then settle into a weekly rhythm. Shock the water weekly and after any heavy-use session.
Frequently Asked Questions
What order do I add hot tub chemicals after a refill?
The correct order is: alkalinity first, pH second, calcium hardness third, shock fourth, and sanitizer last. Adding sanitizer before balancing pH wastes chemical and can leave your water cloudy or irritating. Always let jets run for 15–20 minutes between additions so each chemical fully disperses before you retest.
How long should I wait to get in my hot tub after adding chemicals?
Wait a minimum of 20 minutes with jets running after adding any chemical. After a full start-up treatment (shock + sanitizer), let the spa circulate for at least 2 hours and retest before the first soak. Chlorine should read between 3 and 5 ppm — any higher and you'll want to wait until it drops.
Why does my hot tub water turn cloudy right after a refill?
Cloudy water on a fresh fill usually means one of three things: pH is out of range (most common), calcium hardness is too high, or you skipped the shock step before adding sanitizer. Retest all four parameters, correct what's off, and shock with a non-chlorine oxidizer. Clarity typically returns within 24 hours.
Can I use pool chemicals in my Master Spas hot tub?
No. Pool chemicals are formulated for large water volumes at lower temperatures and are too concentrated for a spa. Hot water also accelerates chemical reactions, so pool-strength doses can damage your heater, cover, and jets. Use only chemicals formulated for spas — browse the full hot tub chemicals collection for spa-safe options.
How often should I shock my hot tub in spring?
Shock weekly for normal use, and immediately after heavy use (a party, multiple consecutive soaks, or anything that introduces extra contaminants like lotion or deodorant). In the first two weeks after a refill, a second mid-week shock helps burn off fill-water contaminants and stabilize your chemistry faster.
What's the easiest way to handle a spring spa opening if I'm new to this?
Buy a complete starter kit. The HT Spa Starter Kit bundles every chemical you need for a fresh fill — pH/alkalinity increaser, calcium booster, chlorinating granules, oxy shock, stain & scale treatment, and test strips — with dosing instructions on each bottle. It takes the guesswork out of your first season and costs less than buying each piece individually.
A properly balanced spa is a spa that takes care of itself — clean water, a heater that lasts, and soaks that feel great instead of making your eyes sting. For every chemical, test strip, and maintenance part you need this spring, shop Master Spa Parts Online. We stock OEM Master Spas parts and chemicals with free shipping on orders over $99, so you can get your spa season started right.