TDS

[waskydiver]

My pool had a rough winter.

A pipe from the filter froze and burst (yea... sloppy closing).This caused about 1/4 of my water to drain, and it was filled with rain water.

Decided to get an early jump on it.

First test showed CYA near 0. (Probably about 10).

So I finally had a chance to use some dichlor that I had lying around.

Added about 2 quarts of acid... got the pH to about normal.

Current numbers are:

15000 Plaster
pH between 7.6 and 7.7
CYA: 30-40
TC: 13
CC: 2
TA: 70
CH: 150

I'm pretty happy with my CYA. I have some trichlor pucks in there to trickle it up some.

I'm going to notch up the TA a bit with some Borax while adding acid to keep the pH in line. Maybe shoot for 80. (Pool store said my borates were 16)

Try to maintain shock level with bleech.

So, yea... I went to he pool store... mostly I wanted to get a reading on my borates. Shocking how off their readings were.

First they said I had 0 CYA. When asking how that could be with the dichlor I added, they said that it is sometimes consumed during the process of eating algea. I asked if it could sometimes take awhile to register... NOPE... was consumed by the algea. I asked if they could do an ammonia test. Nope... no reason to.

My TC was 7.5, with 0 FC. (My test showed I had 13FC with 2CC).

They had 117 TA, where I showed 70.

But, according to them, all of my readings were moot. My TDS were about 3500, and I needed to get them down by replacing 1/2 my water!

Asking why, it was explained that TDS gets in the way of sanitizer, and makes it less effective. (Nevermind that I have taken my water in there in the past, and they were perfectly happy with a CYA of 100).

Anyway, I was wondering if there was any truth to any negative impacts of high TDS. Or if I should just continue ignoring the pool store.

 

[JasonLion]

TDS (total dissolved solids) is essentially meaningless. What matters is what specific chemicals are making up the TDS. Since all of the important numbers can be measured separately you should go by the separate numbers not TDS. You can have a TDS of 35,000 and if it is nearly all from salt you can be just fine. On the other hand you can have a TDS of 1,000 and if it mostly from CYA you can be in big trouble.

Long ago, when no one really knew what CYA did and no one had a CYA test, people noticed that there was a correlation between TDS and chlorine becoming ineffective. This happened because over time CYA tends to rise and likewise over time TDS tends to rise. High TDS was very suggestive that your CYA level had gotten too high. These days, people add lots of chemicals that increase TDS which aren't a problem, like salt, so the correlation between CYA and TDS is much less likely to be true than it used to be. More importantly, you can measure CYA directly and know right away if there is a problem or not, so why bother with TDS which can easily be misleading/wrong.

 

[waskydiver]

Other than CYA, is there anything else that contributes to TDS that I should be concerned about?

 

[JasonLion]

High CH levels can be a problem. If CH is over 500 you need to be careful and adjust some of your other levels to compensate and when CH gets up to around 1,200 to 1,400 you have no choice but to replace water or get an RO treatment.

Salt levels of 6,000 or higher are also a possible concern depending on the materials used in your build. Salt above 6,000 is an issue for some of the softer natural stones and for copper heat exchangers.