Why is the industry standard TA 80-120ppm?

[tomfrh]

The traditional recommendations for alkalinity seems to be 80-120. I've seen recommendations up to 150ppm.

For many years I did this and it put my in a vicuous cycle which required obscene amounts of acid and bicarb. Since adopting TFP I've ran alkalinity at 50-60ppm, which results in much slower pH rise, and barely any need to add bicarb. It seems much more stable.

What's the basis for the traditional recommendation to keep it at 100ppm+?

 

[Summoner12]

To sell you chems.... more chems, more monies, more better.

The traditional recommendations for alkalinity seems to be 80-120. I've seen recommendations up to 150ppm.

For many years I did this and it put my in a vicuous cycle which required obscene amounts of acid and bicarb. Since adopting TFP I've ran alkalinity at 50-60ppm, which results in much slower pH rise, and barely any need to add bicarb. It seems much more stable.

What's the basis for the traditional recommendation to keep it at 100ppm+?

 

[CRAD_oz]

Good question, for the first 18months of owning a pool a followed instructions from the pool shop which included a bag of Alk-up. As a result I went through a drum of acid which was dosed automatically by my Chlorinator.
Now I'm following TFP my pH is stable and the acid drum is still full since last season.

 

[Leebo]

It’ll likely be some time before you see these changed I suspect. The reasoning is because a high TA actually serves a Purpose, to prevent crashing the pH when pucks or Trichlor are used. Seeing how these forms of chlorine are so common, I suspect high TA will stick around for some time.

 

[tomfrh]

Leebo,

how many pools experience pH crashing? Is it quite common?

I’ve only ever had salt pools with plaster walls and its always been a perpetual battle to control pH rise. I have never had pH fall too low on its own.

That’s kinda sad if that’s the reason for the 80-120 rule. It’s a very blunt instrument given how many pools don’t need a buffer against pH crash

 

[JoyfulNoise]

Vinyl & fiberglass pools are most susceptible to pH crash especially when fill water is acidic/low alkalinity in nature (as is the case in parts of the United States). Service companies predominantly use dichlor and trichlor for sanitizer maintenance and so high alkalinity is needed. You also see a bucket of soda ash in the back of most service trucks to help them quickly raise pH and TA when they use too much trichlor. It’s a vicious cycle yes, but one entirely caused by a complete lack of understanding or care. When the primary goal is to spend 15mins or less at a customer pool, corners get severely cut and carelessness is all but certain.

 

[mgtfp]

many pools experience pH crashing? Is it quite common?

When using Trichlor as the main source of chlorine, the risk of a pH crash is real. Each addition of Trichlor reduces the pH, and the subsequent use of chlorine reduces the pH further (in the case of hypochlorite sources of chlorine like bleach but also SWGs, adding chlorine raises pH, and use of chlorine reduces pH again, the cycle is pH-neutral). So, you need enough buffer (i.e. TA) to reduce the pH-change in the first place, and a higher TA with increased CO2-outgassing is actually desirable to counteract the continued pH downward-drift.

But high TA doesn't make sense at all when chlorinating with bleach or a SWG.

 

[ciaka]

My PB asked me to keep TA at where it was (about 250). Initially followed it and ran through a lot of acid to keep pool in mid 7s pH. Then I found this place, worked to lower my TA to 75 (using acid to get to lower 7s pH, then aerate with my water features, to raise pH alone to higher 7s again). Once I reached that 75ppm TA target, my acid use slowed down to pretty much zero. I haven't added any in about a month. I may use it this coming weekend to lower pH by 0.2. At TA 75, my pool seems to have found a great balance. I will continue to be using TFP advice for sure.

 

[JamesW]

how many pools experience pH crashing? Is it quite common?

It's not common, but there are probably thousands of pools with zero TA or less due to using trichlor.

At zero TA, the pH is 4.5.

The pH can go significantly below 4.5.

You would think that people would immediately notice such a low pH, but it's not unusual for people to not notice or not realize that there is a problem.

Some people never test the water for pH or TA and they just keep adding trichlor tabs and they have no idea that they are swimming in very acidic water.

50 lbs of trichlor in a 25,000 gallon pool will:
Raise fc by 219 ppm
Raise CYA by 133 ppm
Raise salt by 179 ppm
Lower TA by 154 ppm

If the pool owner started at 154 ppm or less TA and used 50 total lbs of trichlor without compensating, the TA would go to zero or lower.

If the chlorine demand is 2.19 ppm per day, that's 50 lbs in 100 days.

If the fc demand is 3 ppm per day, that's 73 days of trichlor tabs, which is about 2.4 months.