Q: Hi Rob. Thank you for your column. I’ve actually picked up a few hot tub tips since I started reading it here. So, thank you for that. I actually have a question I’m sure you can answer. The nights have been getting a little cooler, and we have been using the hot tub a lot more. The actual question is why is the hot tub not keeping chlorine. I put it in, and the next day it’s gone. Help! Chris G.

A: Hi Chris! Thank you for reading the articles. I’m also glad you were able to pick up a few tips. Your hot tub is experiencing a “chlorine demand” issue. This means you are in a negative position as it relates to your chlorine.

The easy way to explain this is with an analogy. Suppose your bank account was overdrawn. You add money to your account, but it is not enough to bring the balance to a positive. You keep adding money to your account with good intentions, but it is still never quite enough to bring to the point you are showing a positive balance. This is similar to what’s going on with the chlorine in your hot tub.

Chlorine demand is caused when the organics in the hot tub overtake the amount of sanitizer in the spa. In this case the sanitizer is chlorine. Part of regular spa maintenance is the use of spa shock. In short, chlorine and spa shock work like a 1-2 punch. The sanitizer keeps the water bacteria free, and the spa shock eats up the organics to keep the water clean.

The resolve to your issue is solved with one of two solutions. You can add enough chlorine to break the demand or add extra spa shock. I recommend the latter.

Have a pool/spa question? Happy to answer it. Simply email rob@blackthornespas.com.

Rob Robinson