To reopen a hot tub after winter, drain and refill it completely, flush the plumbing lines first with a pipe-purge product, clean the shell and filter, then rebalance chemistry in this order: total alkalinity (80-120 ppm), pH (7.4-7.6), calcium hardness (150-250 ppm), and sanitizer (3-5 ppm chlorine or 3-5 ppm bromine). Most tubs are ready to soak within 24 hours of starting that process.
If you kept using your hot tub through the cold months, you already know the routine – but a lot of owners shut theirs down or just let it sit untouched from November through March. Either way, spring is a great time to do a full reset. Old water accumulates dissolved solids, biofilm builds up in the plumbing, and a winter’s worth of neglect tends to show up fast once you crank the heat back up. The good news is that a proper startup takes one afternoon and sets you up for months of easy maintenance. If you’re curious what that off-season upkeep looked like for folks who kept soaking, winter hot tub use through the cold months covers that side of things well.
Why You Should Always Start With a Pipe Flush
The biggest mistake people make at spring startup is going straight to draining without flushing the lines first. Your plumbing is full of biofilm – a slippery layer of bacteria, body oils, and organic debris that clings to pipe walls. When you drain without flushing, most of that biofilm stays right where it is and colonizes your fresh water within a few days. That’s what causes cloudy water and persistent sanitizer problems early in the season.
Add a pipe flush or line-purge product to your existing water before you drain. Run all the jets on high for 30 minutes. You’ll probably see some foam or gray gunk surface – that’s exactly what you want out of the tub, not in it. Drain immediately after the flush cycle, while everything is still suspended in the water.
How to Drain, Clean, and Refill the Right Way
Once you’ve flushed the lines, drain the tub completely using a submersible pump or your drain valve. A submersible pump is faster – most 1,500 to 2,000 gallon hot tubs drain in about 20-30 minutes that way versus 45-60 minutes with a gravity drain.
With the water out, do a thorough shell wipe-down using a hot tub surface cleaner or a diluted all-purpose cleaner (not bleach on acrylic). Get into the jets, the waterline ring, and the footwell. Rinse everything well before refilling.
Pull the filter while you’re in there. Rinse it with a hose, soak it overnight in a filter cleaning solution, then rinse again in the morning before reinstalling. If your filter is over a year old or the pleats are frayed or discolored, just replace it. A compromised filter is one of the most common reasons spring water goes cloudy fast.
When refilling, run the water through the filter housing intake (usually marked on the equipment compartment) rather than over the shell. This purges air from the plumbing and prevents air locks in the heater. Fill to the middle of the skimmer opening.
What Is the Right Order to Add Spring Startup Chemicals?
Chemistry sequence matters more than most people realize. Adding things out of order means each chemical fights with the last one you added. Follow this order every time:
- Total Alkalinity first. Target 80-120 ppm. Alkalinity buffers your pH, so if it’s off, your pH will swing around no matter what you add. Use sodium bicarbonate to raise it; muriatic acid to lower it.
- pH second. Target 7.4-7.6. Once alkalinity is stable, pH is easy to dial in. Use pH Up (sodium carbonate) or pH Down (dry acid or muriatic acid).
- Calcium Hardness third. Target 150-250 ppm. Low calcium causes foamy, corrosive water that eats away at your equipment. Use calcium chloride to raise it. If you’re on very hard tap water, test before adding anything.
- Sanitizer last. Add a startup dose of chlorine (3-5 ppm) or bromine (3-5 ppm). With bromine, you’ll want to establish a bromine bank first using sodium bromide before activating with an oxidizer.
Let the jets run for at least 30 minutes after each addition before testing again. Fresh tap water often has metals or off-pH readings that settle out once it circulates and heats up. AquaDoc’s startup kit lines up with this same sequence and is worth keeping on hand so you’re not hunting for individual products at the start of every season.
How Long Does Spring Startup Actually Take?
Plan for about 24 hours from drain to first soak. The actual hands-on time is around 2-3 hours spread across that window. The rest is waiting for the tub to heat back up (most tubs take 8-12 hours to reach 100-104°F from cold tap water) and letting chemicals circulate and stabilize before your final test.
Don’t skip the final test before getting in. Grab a reliable test kit and confirm pH, alkalinity, calcium hardness, and sanitizer are all in range. If your sanitizer is reading over 10 ppm chlorine, wait another hour with the cover off before soaking. High sanitizer right after a startup shock is common and harmless as long as you let it drop first.
Common Spring Startup Mistakes Worth Avoiding
- Skipping the flush. You’ll pay for it within a week when biofilm resurfaces in your fresh water.
- Adding shock before balancing pH and alkalinity. Sanitizers work best at proper pH. Adding shock to unbalanced water is wasted product.
- Not testing source water first. Well water in particular can be high in iron or copper, which stains shells and throws off chemistry from the first fill. If you’re on well water, use a metal sequestrant before adding any sanitizer.
- Reinstalling a dirty filter. A biofilm-laden filter dumps everything right back into your clean water. Clean or replace it every startup.
- Assuming last fall’s chemical test still applies. Fresh water is a blank slate. Test everything fresh, even if you drained and refilled just a few months ago.
For a deeper look at how water chemistry interacts during startup and why some tubs behave differently than others, hot tub questions answered with real stories and science covers a lot of the edge cases that come up in practice.
Frequently Asked Questions
Do I need to drain my hot tub before reopening it in spring?
Yes, in almost every case. Water that’s been sitting all winter – even treated water – accumulates dissolved solids and biofilm that make proper chemical balance nearly impossible. Start fresh with a full drain and refill.
What chemicals do I add first when refilling a hot tub in spring?
Add total alkalinity adjuster first, then pH, then calcium hardness, then sanitizer. Doing it in that order keeps each adjustment stable before you move to the next.
How long after spring startup before I can get in the hot tub?
After adding startup chemicals, wait at least 30 minutes to 1 hour with the jets running before testing. Once pH is 7.4 to 7.6, alkalinity is 80 to 120 ppm, and sanitizer is in range, it’s safe to soak.
Should I clean the hot tub filter as part of spring startup?
Absolutely. Rinse the filter thoroughly, soak it overnight in a filter cleaning solution, rinse again, then reinstall. If the filter is over 12 months old or visibly damaged, replace it before refilling.
What if my hot tub smells musty or like mildew after sitting all winter?
That smell is usually biofilm in the plumbing lines. Run a pipe flush product through the old water before draining, then drain and refill. The flush step pulls out the biofilm that cleaning the shell alone won’t reach.
Spring startup is genuinely one of the highest-return maintenance tasks you’ll do all year. An afternoon of real effort means you spend the next three or four months dealing with predictable, easy-to-manage water instead of chasing problems that trace back to a bad fill. Do it right once and the rest of the season takes care of itself.