How to drain and refill a hot tub
Quick answer
Plan a full change every three to four months (sooner with heavy use). Turn off the power, drain through the spigot or a submersible pump, wipe down the shell, clean or replace the filter, refill with a hose, and rebalance: alkalinity, then pH, then sanitizer. The dosing calculator sizes the fresh-fill chemicals.
No amount of chemistry fixes water that is simply worn out. Draining and refilling resets dissolved solids and stabilizer buildup, and a clean refill balances faster than tired water ever will.
Step by step
- Power off at the breaker so the heater cannot run dry.
- Drain through the spigot, or faster with a submersible pump. Send the water somewhere it will not pool against the foundation.
- Wipe the shell with a soft cloth and a spa surface cleaner. Do not use household cleaners that foam.
- Clean the filter while it is out, or fit a fresh one. See cleaning the filter.
- Refill with the hose, ideally through a pre-filter to cut metals and hardness.
- Power on, heat, and balance: alkalinity into 80 to 120 ppm, pH to 7.2 to 7.8, then sanitizer to target.
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.
Purge the plumbing first
The water you see is only part of the story. A film of biofilm and old oils hides in the pipes behind the jets, and a plain drain leaves it there to seed the next fill. Every few changes, or any time the water has been neglected, run a spa system flush (a line-purge product) with the old water still in, circulate it for the time on the label, and you will often see gunk come up through the jets. Then drain. It is the difference between a fill that stays clean for months and one that clouds in a week.
What helps
A fresh or freshly cleaned filter, and a starter kit so you have alkalinity, pH, sanitizer, and shock on hand for the refill.
Get spa chemical starter kit Get replacement spa filter cartridge
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Common questions
How often should I really change the water?
A common rule sets the interval by use: divide your gallons by three times the number of daily bathers to get days between changes. Most home tubs land around three to four months. See the water change schedule guide for the math.
Should I clean the pipes when I drain?
Periodically, yes. A spa system flush run before you drain pushes out the biofilm hiding in the plumbing, so the fresh fill stays clean longer. Do it every few changes, or any time the water has been neglected.
Can I refill with hot water?
If you have the supply, warm water shortens heat-up time and saves a little energy. Most people just fill cold and let the heater do the work, which the heat-time calculator will time for you.