The complete water care quick-start
If you've just built your cold plunge and the water is fresh, this guide walks you through keeping it that way. For the full deep-dive on water chemistry, see our complete water care guide — this page is the practical quick-start for new plunge owners.
The 4 things you need
- Sanitizer: Ozone generator ($45) as primary + PoolRX mineral cartridge ($79, 6-month) as backup
- Filter: Intex C1500 cartridge filter pump ($89)
- Test strips: 5-way pool test strips ($14)
- Thermometer: Floating pool thermometer ($13)
Total water care setup cost: about $220 one-time, then $5/month for replacement filter cartridges and test strips.
The 10-minute weekly routine
Once your system is set up, ongoing water care takes about 10 minutes per week:
| Day | Task | Time |
|---|---|---|
| Monday | Test water with 5-way strip. Adjust pH if needed. | 2 min |
| Monday/Wednesday/Friday | Run ozone generator 30 min | 0 min (automatic timer) |
| Daily | Skim surface debris (if any) | 1 min |
| Sunday | Inspect filter cartridge, hose off if dirty | 5 min |
| Sunday | Verify water temp with floating thermometer | 1 min |
| Monthly | Replace filter cartridge | 2 min |
| Every 4-6 months | Drain, sanitize, refill | 90 min |
Step-by-step: keeping your water clean
1. Set up ozone
Plumb the ozone generator into your chiller return line. The venturi injector sucks ozone gas into the water flow, where it dissolves and oxidizes contaminants. Run 30 minutes, 3× per week (Monday/Wednesday/Friday is the standard schedule). See our ozone installation guide for plumbing details.
2. Run the filter pump 4-8 hours per day
Your filter pump should run on the same timer as your chiller. Most DIYers set both to run 6 hours overnight (when electricity rates are lower). The filter catches skin cells, hair, and debris that would otherwise feed bacteria and cloud your water.
3. Test weekly
Dip a 5-way test strip into your water, wait 15 seconds, compare to the color chart on the bottle. Check:
- pH: 7.2–7.8 (outside this range, sanitizer works poorly and skin irritation occurs)
- Chlorine (if using): 1–2 ppm
- Total alkalinity: 80–120 ppm (buffers pH swings)
- Hardness: 150–400 ppm (too hard = scale, too soft = corrosive)
If anything is off, add the appropriate chemical (pH Up, pH Down, baking soda, etc.) per the manufacturer's instructions.
4. Add a chlorine residual (optional but recommended)
Even with ozone, most experts recommend a small chlorine residual (1–2 ppm) as 24/7 backup protection. Use a slow-dissolving trichlor tablet in a floating dispenser — one tablet lasts 2–3 weeks in a 50-gallon tub. If you can smell chlorine on your skin after plunging, the level is too high.
5. Replace filter cartridge monthly
Pull the cartridge, hose it off weekly (takes 2 minutes), and replace it monthly. A dirty cartridge restricts water flow, which reduces chiller efficiency and creates dead zones where bacteria thrive. Replacement cartridges cost about $5 each on Amazon.
6. Drain and refill every 4-6 months
Even with perfect care, total dissolved solids (TDS) accumulate over time. After 4–6 months, your water will be "tired" — test with a TDS meter (under $10 on Amazon); if TDS is above 1500 ppm, it's time to drain.
To drain: turn off chiller and pump, attach a garden hose to your bulkhead drain fitting, drain to a safe location (not storm drains — chlorinated water harms aquatic life), wipe down the interior with a 10% bleach solution, rinse, refill. Total time: 60–90 minutes.
Signs your water needs attention
| Symptom | Likely cause | Fix |
|---|---|---|
| Cloudy water | Low sanitizer, dirty filter, high pH | Test and adjust chemistry; clean or replace filter; shock with extra ozone |
| Green tint | Algae growth | Add PoolRX or chlorine; run filter 24 hours; brush tub walls |
| Strong chlorine smell | Chloramines (chlorine + sweat) | Shock with extra ozone; partial drain and refill |
| Slippery tub walls | Biofilm | Brush walls, shock with chlorine, run filter 24 hours |
| Foam on surface | Body oils, soap residue | Add defoamer; shower before plunging |
| Musty smell | Bacteria growth | Shock with chlorine; replace water if persists |
The single most effective water care step is also the simplest: a 30-second rinse shower before plunging. Body oils, sweat, deodorant, and sunscreen are the primary food source for bacteria in your plunge water. Rinsing removes 90% of these contaminants. If you plunge daily, shower before every session - your water will last 3x longer.
For the full water chemistry explanation (ozone vs chlorine vs bromine, pH management, TDS, drain schedules), see our complete water care guide.