TDS Test Strips

[jbequer]

What is the best way to know when the water needs to be changed , other than waiting to have nasty water , or when too many chemicals need to be added to do the job ? Are the TDS test strips worth while and are they an accurate indicator for water change ?

I am currently using the 3 to 4 month water change. I would like a better way if there is one, this is why i was thinking of using the TDS test strips. I have been reading mixed reviews on these, some say they are accurate and some say not to bother with them ??
I know there is a formula, but it doesn't really seem to go with my usage which is always changing with kids, friends and family, its never the same from week to week.
Recommended water change about 1500 PPM TDS reading, is this correct ?
I know there are professional digital TDS readers, but they are way too expensive..

Any thoughts ?

[chem geek]

Unless your spa usage is very low, you shouldn't be getting to 1500 ppm TDS before you need to change the water.  1500 ppm TDS as sodium chloride salt would accumulate from 1820 ppm FC cumulatively added so with no spa usage that would be many years of maintaining the chlorine level.  If you add acid frequently to the spa (and probably baking soda as well) then the TDS will rise faster, but TDS as salt is not a reason to change the water.

Instead, you should notice that your water gets somewhat dull looking, may foam significantly more in spite of your best efforts at avoiding soap in the water, may have more scum at the waterline, or may show an increase in chlorine demand beyond normal amounts to handle bather load or in-between-soak maintenance amounts.  Basically the main reason to change the water is a buildup of unoxidized organics not handled by chlorine (or ozone, if used) or filtered out.

The rough rule-of-thumb is the following Water Replacement Interval (WRI) applicable when soaking in a hot (104ºF) spa using the Dichlor-only method:

WRI(days) = (1/9) x (Spa Size in Gallons) / (# of Person-Hours Per Day)

With the Dichlor-then-bleach method you should be able to go about twice as long as the above formula (so use 2/9 as the factor in that case).  If you have high bather load (i.e. soaking nearly every day) then an ozonator helps.

[Vinny]

There's nothing like soaking in newly filled water. Trying to keep water longer just doesn't make sense at times. If it's below zero, yep keep it going but under normal conditions change the water.

Just my opinion.