Total Dissolved Solids

[fdegree]

I am still quite new to all of this water chemistry stuff, so there are a few things that I don't have a full grasp on. One of them being Total Dissolved Solids (TDS). Therefore, I have a few questions:

   1. What is Total Dissolved Solids?
   2. What contributes to TDS?
   3. How do you measure for TDS?
   4. What is the high limit where I should consider changing the water?
   5. If the TDS is below this limit, does the water truly need changing, even if it is beyond the recommended duration since the last fill...say, a year has passed?


Thanks!!!

[tony]

I am still quite new to all of this water chemistry stuff, so there are a few things that I don't have a full grasp on. One of them being Total Dissolved Solids (TDS). Therefore, I have a few questions:

   1. What is Total Dissolved Solids?
   2. What contributes to TDS?
   3. How do you measure for TDS?
   4. What is the high limit where I should consider changing the water?
   5. If the TDS is below this limit, does the water truly need changing, even if it is beyond the recommended duration since the last fill...say, a year has passed?


Thanks!!!

Total dissolved solids are residuals dissolved or residing in the water that don't get filtered filtered out.  It is like a glass of water that you add sugar to.  One teaspoon dissolves quickly but you know its there because the water is sweet.  Add more and the water quality changes and ultimately it will cloud up.

Almost everything we add to our water contributes to TDS from chems to soaps and oils from suits, etc.  Organics get destroyed by sanitation and disappear by way of shocking and filtration, but other byproducts remain.  The largest contributors to TDS are santizers (chlorine, bromine, etc) and non chlorine shock because you add them on a regular basis.  Dichlor, for instance, adds about 1 ppm cyanuric acid for each ppm chlorine.  All the CYA remains as TDS.

There are test kits and strips to test for TDS.  I am not sure how accurate the strips are.  I have never tested for TDS, but you can see and "feel" it in your water.  I have found that my water deteriorates slowly over time so I can't really tell.  Then I change my water and you immediately see the difference.

The high limit, as a general rule, is 1500 ppm.

If your TDS is below 1500, you probably don't need to change your water unless you are using a stabilized chlorine, such as dichlor, because CYA like TDS can only be lowered by removing old water and adding new water.  I have been experimenting with bleach this past winter and just changed my water after five months.  I found no difference in the new water and I believe it is because of greatly reduced TDS and of course CYA.  I have never seen this in my water, so I will continue for another season.  Though I am trying this and have had good results, I am not trying to convert anyone to this method.  It is an experiment for me, my spa is out of warranty and I always had good luck with dichlor, even with very high CYA levels.

[Vinny]

1 TDS is all the stuff in the water that has been added or occurs naturally.
2 Skin cells, bacteria, pollen,used chemicals, added chemicals, soaps from suits ...
3 Don't bother. Follow the rule of dumping the water every 3 to 4 months and you'll be fine.
4 It is 1500 over the starting TDS.
5 3 to 4 months. Do NOT go a year. Going into a tub by yourself is like 20 people going into a pool.  The equation for changing water is: # of days = (1/3 volume of water)/(max # of daiy bathers). So if you only have one person use the tub every day and you have a 500 gallon tub - (1/3 x 500)/ (1) = 167/1 = 167 = max 5 months but if other people go in that will go down drastically. Also the feel of new water is a great experience.

[fdegree]

Thanks for the input...it is truly helpful.

I've had my tub for about 8 months now, and I have dumped 3 times.  Taking into account the rule-of-thumb -- dumping every 3 - 4 months, it is about due for a refill now.  After reading tony's and vinny's posts, I'm wondering if I can stretch this water out a little longer for 2 reasons:

1.  I use bromine as the sanitizer and shock the bromine bank with liquid bleach...I guess that means no CYA, and comparatively speaking, less TDS (or am I misunderstanding)
2.  Infrequent usage...My wife and I are lucky if we have the chance to use it twice a month.

I check the TA, pH, and bromine levels about once a week.  I rarely have to add anything (have bromine floater).  Probably due to the infrequent usage.

I completely understand that it is a good idea to change the water and keep it relatively fresh.  But, since I don't add much and don't use it much, can I get away with longer intervals between refills?  And, if it is reasonable to extend the time of refills, what indicator should I be using to tell when it is time to dump?


Thanks Again!!!