TDS Discussion

[Richard320]

Dunno if this will cause sand to pass through or not but you have a huge crack in your sand filter tube. The water comes up that tube and trinkles down so it shouldnt matter as long as the bottom is in tact.

Have your tds level checked as well. Taylor makes a nice kit or you could have a store test it. If your tds is very high chlorine wont do much to clear that water you'd have to replace with fresh water.

Just what ARE these TDS? And why are they so dangerous? And how come I've managed to maintain a crystal clear algae-free pool for three years solid , nights, weekends, and holidays included without ever once knowing what my TDS level is?

You're In the Industry - explain this, please.

 

[Matt Ush]

Re: Undissolved Chemicals

Dunno if this will cause sand to pass through or not but you have a huge crack in your sand filter tube. The water comes up that tube and trinkles down so it shouldnt matter as long as the bottom is in tact.

Have your tds level checked as well. Taylor makes a nice kit or you could have a store test it. If your tds is very high chlorine wont do much to clear that water you'd have to replace with fresh water.

Just what ARE these TDS? And why are they so dangerous? And how come I've managed to maintain a crystal clear algae-free pool for three years solid , nights, weekends, and holidays included without ever once knowing what my TDS level is?

You're In the Industry - explain this, please.

I actually did not make my title to say In the Industry..I guess an admin did. But anyway, from what I understand, if your total dissolved solids is high enough, the only way to decrease it is to replace with fresh water. If your total dissolved solids is high enough, the chlorine you add to the pool would be less effective as the water would have a harder time absorbing the chemical. We serviced a pool that had a sewer flood into the pool. pH, alk, calcium, sanitizer and CYA were all in check as well as 24/7 filtering and backwashing. No matter how much chlorine we dumped in, the water was a green swamp. The tds tested over 5,000ppm. Please correct me if I am wrong.

Of all the pools I serviced, I've only had tds appear to be an issue twice.

This article actually proves me wrong so I'd like to hear more opinions. http://ppoa.org/pdfs/What%20is%20the%20 ... Solids.pdf

 

[chem geek]

That article is from the PPOA who are often right, but not always. In this case they are right. TDS by itself doesn't matter. It's what TDS is composed of that matters. In your example about not being able to hold chlorine you can't just say all the levels were OK because I'm pretty sure you didn't know about the chlorine/CYA relationship at the time you had trouble with the two pools, did you? So you didn't know that if the FC was not high enough relative to the CYA level then algae could grow faster than chlorine could kill it, creating high chlorine demand so chlorine could not be held.

We have not had a single green swamp on this forum that was not turned around with chlorine alone (physical removal of leaves and other material is done in truly swampy pools), though those with high CYA levels often had their water partially replaced to lower the CYA; otherwise the amount of chlorine needed would be impractical. Also, a single dumping of a lot of chlorine into the pool is not the proper way to shock. One must maintain a high FC/CYA ratio to shock a pool.

Now in high bather-load pools such as commercial/public pools, a high TDS well above initially added chemicals (TA, CH, salt) can be a proxy for the chemicals accumulated from bather-load and some of these do not get readily oxidized by chlorine so if they build up then they can increase chlorine demand. Also, such pools often have sand filters and can get biofilms in them which also increase chlorine demand. Residential pools, however, don't have these sorts of problems, especially not having TDS be a problem since the bulk of TDS is just plain sodium chloride salt.

The next time you run into a green swampy pool that doesn't seem to respond to chlorine, walk us through it here. Odds are the CYA is through the roof and that is the real cause of making the chlorine less effective, not the TDS which is mostly salt.

 

[Patrick_B]

It's what TDS is composed of that matters.

Absolutely!

As for pools this IS all that matters. TDS and Conductivity mean nothing except to Salt analyzers, and they measure salt levels based on conductivity if I am not mistaken. As for pool water testing results, TDS and Conductivity are irrelevant in my view. However, we do use conductivity (usually) in the industry to control mineral concentration levels (cycles of concentration) in cooling towers and boilers. Easier to do than trying to control based on hardness analyzer readings etc. It works because we know that at various conductivity levels, our hardness level will be....say 300 CH, and Conductivity of 3000, at three cycles. This is because it is 100 CH with 1000 Conductivity incoming. We cycle it up three times and there you go. That can change based on incoming water, but more often than not it is pretty stable.

Life for us would be much more difficult if we couldn't rely on conductivity readings for control, but TDS for pools, not very helpful.

Why they give this number out is beyond me because it is pretty worthless to a pool owner. I say this because you could have a well balanced pool and TDS would tell you nothing about that. You could have a "high" or "low" number, and a perfect chemical balance. Who says what is a good number? If my TDS were "too high" and I was balanced well, what then? Should I bring it down? Nope. I think it is fluff they add to your results. Means nothing practical.

So there you go, you asked from someone in the industry...that's my .02 worth. (No charge for you Richard) :lol:

 

[ngc4900]

Hi,
I read that PPOA article on TDS today. Up until that point, TDS wasn't even in my vocabulary and I have had my pool for 3 years. I am going to read the pool school here. I have questions about SI as well.
Thanks
Joe

 

[Patrick_B]

Hi,
I read that PPOA article on TDS today. Up until that point, TDS wasn't even in my vocabulary and I have had my pool for 3 years. I am going to read the pool school here. I have questions about SI as well.
Thanks
Joe

Good for you! Doing that, and gaining understanding is the most important thing you can do. Feel welcome to ask questions in the forum should you have any. Teaching and learning is what we are all about here.