There’s nothing quite like the feeling of sinking into a hot, bubbling spa after a long day. The warm water, the powerful jets, the complete relaxation, it’s a little slice of paradise in your own backyard. But over time, even the most meticulously maintained spa water can become tired and uninviting. This “worn-out” water is a common issue for hot tub owners, and recognizing the signs is key to maintaining a clean, healthy, and enjoyable spa experience.
So, how do you know if your hot tub water has reached its limit? In this guide, we’ll reveal the clear signs that it’s time to drain and refill your spa, explain the science behind why water wears out, and provide a simple formula to help you determine the right schedule for your specific needs.
The Silent Culprit: Total Dissolved Solids (TDS)
Before we get to the symptoms, let’s talk about the root cause. The reason your spa water eventually “wears out” has a scientific name: Total Dissolved Solids (TDS).
TDS is the measure of all the dissolved organic and inorganic substances in your water. Think of it as a soup of everything that’s ever entered your spa. This includes minerals from your tap water, residual sanitizing chemicals, bather waste (like body oils, lotions, and soaps), and other environmental contaminants.
While your filter removes suspended particles, and your sanitizer kills living organisms, TDS accumulates over time. As TDS levels rise, your sanitizer’s effectiveness plummets. It becomes harder to maintain balanced pH levels, and a shock treatment that used to clear the water now seems to do very little. High TDS is the primary reason for most of the frustrating problems you’ll encounter.
The 5 Tell-Tale Signs of Worn-Out Spa Water
You don’t need a lab test to know when your hot tub water is past its prime. Your senses and the behaviour of your water will tell you everything you need to know.
1. The Water is Consistently Cloudy or Murky
This is the most common and visible sign that your water has reached the end of its life cycle. You’ve balanced the pH, added sanitizer, and even shocked the water, but no matter what you do, it just won’t stay sparkling clear. This persistent cloudiness is a direct result of a high TDS level. Your sanitizer can no longer work efficiently to clear up the microscopic particles, and your filter simply can’t keep up with the buildup.
2. There is a Pungent, Unpleasant Odor
A common misconception is that a strong chemical smell means your spa has too much chlorine. In fact, the opposite is true. That distinct “hot tub smell” is caused by chloramines, which are chemical byproducts that form when free chlorine combines with bather waste. High levels of chloramines signal that your sanitizer is being overwhelmed and the water is no longer clean. If your spa smells like a locker room, it’s time to drain and refill your spa.
3. The Water is Foamy and Won’t Go Away
When you turn on the jets, a little foam is normal. However, if that foam takes a long time to dissipate, or if it’s thick and greasy, it’s a sure sign that your water is full of contaminants. The foaming is caused by a buildup of surfactants from soaps, detergents, body oils, hair products, and lotions. While a foam reducer can provide a temporary fix, it doesn’t remove the contaminants. It only masks the problem, and the foam will return as long as the underlying issue of high TDS remains.
4. You Experience Skin or Eye Irritation
If your skin feels dry and itchy, or your eyes sting after using the hot tub, the problem is most likely your water, not a chlorine allergy. Just like with the unpleasant odour, this irritation is typically caused by high levels of chloramines and other contaminants that are overpowering your sanitizer. Draining and refilling the spa with fresh water is the fastest and most effective way to eliminate these irritants.
5. Your Chemicals Just Aren’t Working
This is a key indicator for any seasoned spa owner. You’re constantly adding pH balancers, sanitizers, and alkalinity boosters, but your water chemistry remains wildly unpredictable. The levels don’t hold, and it feels like you’re fighting a losing battle. This is a classic symptom of high TDS. The dissolved solids are interfering with your chemicals’ ability to work, making a balanced spa water maintenance routine nearly impossible. When this happens, it’s a clear signal that the water is completely saturated and needs to be replaced.
The Right Time to Drain and Refill: The Bather-Load Formula
So, if you’re not going by the tell-tale signs, how often should you change your spa water? The simple rule of thumb is every 3 to 4 months. This is a good guideline for an average-use spa.
However, a more precise method that accounts for your specific usage is the bather-load formula. This formula helps you calculate the optimal drain and refill schedule based on how many people use your spa and how often.
The Bather-Load Formula:
(Spa Capacity in Gallons) / (Number of Daily Bathers x 20) = Days Between Draining
Let’s use an example to make this easy:
- Your Spa Capacity: 350 gallons
- Average Daily Bathers: 2 people
- Calculation: 350 / (2 x 20) = 350 / 40 = 8.75 days
This calculation shows that for this specific usage, you should drain and refill your spa every 8 or 9 days. While this seems frequent, it highlights just how quickly water can get saturated with heavy use. For most households, with less frequent use, the number will be much higher, closer to that 3–4-month average.
The Quick Guide to Draining and Refilling
Once you’ve determined it’s time for a refresh, here’s a quick, step-by-step guide to get your spa back in peak condition:
- Turn Off the Power: Go to the main breaker and completely turn off the power to the spa to avoid damage to the pump.
- Drain the Spa: Use the built-in drain valve or a submersible pump to quickly empty the water.
- Clean the Spa Shell: Use a non-foaming hot tub shell cleaner and a soft cloth to wipe down the surface, removing any built-up residue.
- Clean or Replace Filters: Remove your filters and either clean them thoroughly with a filter cleaning solution or replace them if they are old. Clean filters are crucial for proper water circulation.
- Refill with Fresh Water: Use a hose to refill the spa. It’s best to run the hose into the filter housing to help push any air out of the plumbing lines.
- Balance the Chemicals: Once the spa is full, power it back on, heat it to the desired temperature, and then add your chemicals in the correct order to balance the pH, alkalinity, and hardness.
- Sanitize: Add your preferred sanitizer (chlorine, bromine, etc.) to start the new cycle of keeping your water sparkling and clean.
By paying attention to the signs and following a regular drain and refill schedule, you can ensure your spa remains a perfectly clean and relaxing retreat all year round. It’s the single most important part of a truly effective spa maintenance routine.