Total Dissolved Solids question


Aug 18, 2015
I have a question pertaining to total dissolved solids(TDS). The chemical companies literature says once it's >1500 it's time for a water change and the spa mfg and spa shop say when it's >2500 it's time for a change. I've spent hours upon hours reading this forum and see very little mentioned about it at all, plus my Taylor test kit doesn't mention it either. So I'm wondering how important is it really, if at all? I plan on changing my water every 3-4 months no matter what. So, is this something I even need to think about? Let me know your opinions.


TFP Expert
Feb 3, 2014
Central Minnesota
It's an irrelevant number. A well-maintained spa can be use for at least 3 months before a water change. Don't worry one bit about TDS. TDS is a number that is the sum of many other chemicals in the pool such as CYA, CH, salt, etc. Therefore, it's not very meaningful. Knowing the concentration of the individual chemical species is important.

Stick to your 3-4 month plan as long as you always keep some FC in the tub and see the two stickies in this forum for our recommendations on chlorine or bromine spas.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Joel nailed the executive summary - don't worry about it.

TDS was used in the past as proxy for how much "stuff" was on your water. Prior to cheap and reliable test methods for individual ions and chemicals, TDS was a way to quantify the quality of your water. The true way to measure was to take sample of water and evaporate/dry all the water from it and measure the weight of all the left over solids. Electronic methods eventually supplanted dry weight measures.

Like so many things in the pool/spa industry, change and adoption of new standards is very slow. To this day, the effects of CYA on FC are still largely ignored even though the science has been established and proven for over 30+ years. Manufacturers are locked into regulations that haven't been updated in decades and are forced to quote "recommended levels" even though they make no sense or have little factual justification.

Now, I command you, go and enjoy your spa :D !!

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