Help understanding "balanced water"

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Daf-Tekno

Daf-Tekno

0
Sep 14, 2014
90
Calgary / AB
Split by moderator from the sticky HERE. Please do not hijack; start your own thread. Thanks, jblizzle

Hi guys,

This thread mentions:
"...The lower the CH, the higher the TA & pH must be to have 'Balanced Water'..."
"...The lower the TA, the higher the pH must be to have 'Balanced Water'...".

Are there graphs anywhere that correlate CH to TA (& pH) and TA to pH?

If I'm operating my spa at CH 100, what should my TA & pH be to be 'Balanced'?
If I'm also aiming to have my TA at 50 along with my CH at 100, is my pH to be different to the usual 7.4 - 7.6?

Thanks - D
 
Re: How do I use Chlorine in my Spa (or pool)?

There aren't graphs, but you can adjust the numbers in PoolMath to see how things change the saturation index. In short, the following describes how each parameter affects the saturation index:

  • pH directly affects the saturation index so an increase of 0.1 in pH increases the saturation index by 0.1
  • Adjusted TA (roughly 1/3rd of CYA subtracted from TA) logarithmically affects the saturation index so every doubling the TA increases the saturation index by 0.3
  • CH logarithmically affects the saturation index so every doubling the CH increases the saturation index by 0.3
  • TDS or Salt inversely affects the saturation index a relatively small amount where an increase in TDS or Salt decreases the saturation index
  • Temperature somewhat affects the saturation index where an increase in temperature increases the saturation index
You generally set your TA level so that the pH is more stable so in a spa that's usually around 50 ppm (before adding borates) and you probably have around 30 ppm CYA. Figure your pH target will be around 7.7 unless your pH is fairly stable lower than that. You normally need around 120-150 ppm CH to prevent foaming. The spa temperature is up to 104ºF. This combination has the saturation index be around -0.2 which is fine since 1) you don't want scaling in the heat exchanger and it's generally 30ºF hotter and 2) you don't need to saturate the water with calcium carbonate (i.e. you don't need the saturation index to be 0) unless you have a plaster surface or grout in tile exposed to the water.

If you find that your pH tends to rise, then I wouldn't try to maintain it any lower than 7.5 and instead see if it settles in better at 7.7 or 7.8. Note that after you add the borates, the TA will be higher. At pH 7.5 the 50 ppm Borates (at 104ºF) will raise the TA by around 8 ppm while at pH 7.8 the TA is raised by around 15 ppm. Do not worry about adjusting the TA lower after adding the borates unless for some reason the pH is still rising too quickly.
 
Hi ChemGeek,

Thanks for the figures.

My TA is currently 40, so if I now added the borate 'mix', after it's settled down, my TA may actually end up around 50.
So, should I add the borates now with a TA of 40, or get it up a little higher to 50, then add the borates..?

Thanks - D
 
Hi again,

The guys at Controlomatic sent me this amendment to the suspiciously out of date water balance requirements given in their instruction leaflet:

"...Regarding the calcium hardness and TA level. The 130 to 150 hardness and your TA of 50 would be fine if you keep your pH below 7.4 and your sanitizer between 3-5 ppm.
When you allow those parameters to move, you can have your hardness go from neutral to acidic and that will cause you problems.
We recommend CH 300-400 to be on the safer side...".

"...just make sure that overall your water balance is neutral or slightly on the scale forming side.
It is better to have to remove a little calcium from the titanium plates than replace parts in your spa like the heater...".

I think they're fine with these levels, but I'm not sure if I can make pH < 7.4.

- D
 
Unless your spa is made of plaster or concrete or tile, to something else that is held together with plaster or grout, then there is no advantage, and many disadvantages, to being "Balanced". The kind of balanced you are talking about is only important in association with plaster/concrete/grout surfaces. In all other situations you want the water to be out of "balance" low to avoid calcium scaling.

Also, many of your questions are closely interrelated. You really ought to keep them all together in one place, as the context of what you have said before is very important to help answer your questions.
 
The ControlOMatic guys don't really know what they are talking about. First of all, in a spa the water temperature is hotter and at 104ºF the Calcite Saturation Index (CSI) is about 0.2 higher than at 80ºF. They wrote

When you allow those parameters to move, you can have your hardness go from neutral to acidic and that will cause you problems.
Click to expand...
where presumably they mean "balanced to corrosive" referring to the saturation index and they wrote

It is better to have to remove a little calcium from the titanium plates than replace parts in your spa like the heater...
Click to expand...

Corrosion in the heater does NOT come from not saturating the water with calcium carbonate. That is a misconception in the pool/spa industry. While some municipal water systems can try to coat their pipes with a thin layer of calcium carbonate for protection, it is very hard to do when the temperature varies (as it does in a spa) and flow rates vary (as it does when the pump cycles). See this link for a discussion among corrosion experts on this topic. Basically, low pH is the primary corrosion problem. High oxidizer levels are also a problem, so chlorine in the spa with no CYA would be more corrosive due to the higher active chlorine level and is yet another reason why some CYA should be used in the spa (the ControlOMatic guys don't know about that and as a result probably have experienced more corrosion in heaters -- due to the higher active chlorine level from not having any CYA in the water).

Check your tap water that goes through copper piping. Mine has a pH of 7.7, TA of 80, CH of 55, Temp of 67ºF, for a saturation index of -0.6 yet the pipes do not corrode. They do add 300-500 ppb orthophosphate to the water to help inhibit corrosion, but they do not try and saturate the water with calcium carbonate. Such saturation is needed to protect plaster pool surfaces and grout in tile, but is not needed to prevent metal corrosion. Furthermore at the numbers we've recommended, the saturation index at 104ºF is around -0.2 but at the heater when it's on with a 30º higher temperature at the heat exchanger surface the saturation index is around 0. It is far more likely for you to get scale in your heater if the saturation index is high than for it to corrode if the saturation index is low (unless it's low due to low pH since that is the primary factor for corrosion).

The bottom line is that you should NOT mix advice from different sources. Why did you even ask them for what they thought about your water parameters? You need to decide whose advice you are going to follow. As Jason has told you before, you should not mix advice or you will get into trouble.
 
Hi TFP Seniors,

I mentioned the Controlomatic response to have their views interpreted and also to see what you guys made of their position.
I have no intention of mixing advice. I initially tried to aim for an area where everyone agreed, but as I was basing this on Pool numbers rather than Spa numbers, it was clearly a flawed angle.

As I added a shed load of calcium the first fill a week ago (to get to CH 300), I was concerned at the physical size of what I was adding, already making me doubt the SWG's guidelines.

Even though the level of chemistry you guys talk on is way beyond my comprehension, it is quite clear that you base your views on science fact and real-world experience.
Another sign that you guys speak the truth is your willingness to convey it to the less enlightened.
I have always found this to be a sign of true sincerity in my quest through life so far, and as such endorses your advice with the highest accolade.

I also wanted to see if the Controlomatic guys responded with something like, "For God's sake, don't operate our SWG at those levels!".

I wish I could combine my multiple questions into 1 or 2 threads, but as each one is asking something fairly specific, it seemed logical to fire them off individually.
I'm trying my best to fit my queries into the bigger shape of the forum, but as with the BBB system, I'm on a bit of a learning curve!

Please accept my profuse apologies if I have annoyed any of you Aqua-Masters.

Sufficed to say, my Spa is settling down with the amended levels of CH 120, CYA c.30, TA 50, pH 7.6 - 7.8, FC c.3.0 / CC c.0.2, Salt 2000, Borate 50.
We even managed to find Boric Acid (in powder form) at Shoppers Drugmart, although not in time for this refill, so Borax / acid it is for now.

I suspect things are starting to look up...

Many thanks and Best Regards,
- D
 
Hi Chem Geek,

Thank you (and you other guys) for sharing your vast knowledge of water chemistry with the lowly likes of myself.

One thing to mention on my water chemistry:
I've always left my Spa's waterfall running on low, as recommended by Jacuzzi Calgary to ensure it has no stagnant water in its lines.
But, as this will be constantly aerating the water to some degree, my pH will be tending to increase as a result.

However, Nitro's thread on Chlorine use in Spas mentions that you should keep lowering your TA until your pH won't rise above 7.6, not matter how long you aerate for.
So, if my TA is 'perfectly tuned', my pH can't go over 7.6, even if I leave my waterfall running 24 / 7.

But as you point out, Chem Geek, I may end up having 7.7 - 7.8 as my 'pH norm', so I'm not sure of the validity of 'perfectly tuned' TA in my Spa.
I also wondered if it's generally viewed as good or bad practice to leave the waterfall running in a Spa.

Many thanks - D
 

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They don't want the water to be stagnant since pathogens can grow in that situation. If you can reduce the volume of water going through the waterfall, that will help. "Low" sounds good.

Having the pH settle in (or slow down in its rise significantly) at 7.7 or 7.8 is not a problem. And yes, you may not be able to have a TA that stops the pH rise if you have aeration from the waterfall. Technically, at a TA of 50 ppm with 30 ppm CYA and 104ºF the pH won't rise above 8.0, but it should slow down significantly below that pH. I wouldn't worry about it. Just get things to a point that works for you.
 
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