When to change the water...

[fletch49]

Hey all - I was at the local spa dealer the other day, and was enquiring about when to change the water. The dealer used a simple calculation to determine when I should change the water.

It was like...'total#bathers'/3*'total use'. Anyway, based on my usage, it came out to something like every 74 days, I should change the water.

I didn't write the calculation down. Does anyone know of a similar way to calculate when the water should be changed?  Untill I go out and purchase a TDS meter, I wonder if this will suffice?

Thanks

[Brewman]

I go by a rule of thumb of every three months or so, but the water I have now is from early November- mid winter water changes are not something I'm going to attempt.  Bill does partial water changes, which are a good idea.  
You'll know when it's time to change your spa water after you've owned your spa a few months.  

A lot depends on your bather load (and how much goo is introduced to the spa), and other usage patterns.
You'll figure this out as you go along.

Brewman

[Bill_Stevenson]

I believe the formula you are looking for is:  Spa size in gallons divided by the the number of daily bathers times 3.  

[wmccall]

I use partial changes a lot in the winter when I don't want to have to wait for 400 gallons to come from 40 degree to 104.  I will also do so when conditions go bad for what ever reason and it has been less than 2 months since my last change.  I shoot for 3 months, but my primary indication is a lot of effervence when the jets are running and it takes more than 15 seconds for the water to clear after turning the jets off.  Most of the time even at 3 months, my water looks and smells ok when you first open the cover, but after awhile, your experiences eye will see differences.

[PPOL]

I use and tell my customers that they should drain about every 4-6 months, depending on water quality.

You can tell after about 4 months, the water takes more and more chemicals to treat and there is an odor to the water.  Play it by ear once you get used to the tub.

[Chas]

Once at the end of the first thirty days, and then every three or four months.

Works for just about all spas.

And some marine aquariums too...

[fletch49]

Actually, just after I wrote that, I recieved the answer to my question. Over night my water went from OK to bad.  Up to that night, the water was very slowly taking more chemicals to balance and the clarity was slowly getting worse...not cloudy, but not sharp, and no smell, but I was still able to manage the water.
My wife and I had another couple over for about a 2 hour soak (aka, the three martini soak) and that made the water flip flop from OK to bad. THat night, I excessively shocked the water and went to bed, the next day I checked the water and it was done. Cloudy, smelly, foamy...stick a fork in it, it's done.

I guess my question now is, does it normally go bad that quick? Or should 4 adults (I use the word loosely) not spend that much time in a 400gal tub?