The following method assumes 6.8 is the lowest measurement on your pH test kit:
|Step||Action to Take||pH||TA||Notes|
|1||Add Acid||lowers||lowers||Add enough acid to bring pH down to 7.0|
|2||Aeration||raises||none||Aerate until pH rises to 7.2|
|3||Add Acid||lowers||lowers||Add acid to bring pH down to 7.0 (continue to aerate)|
Aeration & Acid
|none||lowers||Repeat steps 1 & 2 until TA reaches the target|
then AFTER you have reached your target TA
|5||Aeration||raises||none||Aerate until pH rises to your target (say, 7.5)|
chem geek wrote:Neither the acid ball slug method nor the drizzling method are the same thing as lowering the pH significantly and then adding aeration while adding acid to keep the pH low. Even if the acid ball slug method is somewhat more effective at lowering TA (and this is controversial), it is not nearly as effective as low pH with aeration. This is the fastest way to lower TA -- guaranteed. It is the following procedure. Note that you should use the next to lowest measurement on your pH test kit as the low-end -- so if your pH kit only goes to 7.0, then use 7.2 as the low-end target and 7.4 as the high-end trigger to add acid to get back to 7.2.
ACTIVITY .......... pH .... TA ... The following assumes 6.8 is the lowest measurement on the pH test kit
Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0 (if it's already there, then just skip to the next step, aeration)
Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2
Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want
then AFTER you have reached your target TA,
Aeration .............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).
Net of Above ....... 0 ........ -
Note that there is NO addition of base (Borax or otherwise) in the above procedure. Aeration would include running your SWG, running your waterfall, adding any fountains or other aeration features, getting an air compressor with a nozzle or pipe with small holes that produces tiny bubbles and putting that in the deep end of the pool, etc. By the way, rain is an excellent aerator with splashing drops, but unless you can control the weather...
The above procedure works because the rate of outgassing of carbon dioxide from a pool varies with pH and TA level and with aeration. Pools are intentionally over-carbonated -- that's why you initially add sodium bicarbonate / baking soda / Alkalinity Up on pool startup (unless your fill water is already high in Total Alkalinity). Think of the pool as a carbonated beverage -- it will outgas carbon dioxide. Stirring up (aerating) your drink causes more carbon dioxide to release faster. If you blow bubbles through a straw, the drink goes flat (loses its dissolved carbon dioxide) quite quickly. If you measured the pH and TA of your drink, you would find that as carbon dioxide is released, the pH rises with no change in TA. The same happens in a pool (for technical reasons I won't get into here).
This chart shows the relative carbon dioxide outgassing rate at various pH and TA levels. This is a relative rate since it is also a function of aeration, wind, etc. and that is not easily quantifiable. You can see how lower pH significantly increases outgassing. That's what makes the above procedure go faster, along with aeration. The outgassing rate also determines the amount of acid you would need to add over time to restore (lower) the pH. So running your pool at lower TA and higher pH will lessen the need for acid addition over time.
This chart shows the relative rate of pH rise at various pH and TA levels. Though the lower TA has a lower outgassing rate, it also has a lower pH buffering effect and these tend to cancel each other out though the outgassing effect is slightly stronger. This is why you can see some lowering the the pH rise at lower TA though running at a higher pH target is more effective (so most people do both -- lower their TA level AND target a higher pH).
This was the classic method, now debunked:
Here is a step by step guide to reduce the Total Alk of swimming pool water:
- Turn off the pump and wait at least half an hour for the pool water to stop moving.
- Choose an open spot in the deep end of the pool and pour the required amount of pH reducer slowly into this one spot. If you are using granule or powder pH reducer, first dissolve it in a bucket of water.
- The water will become hazy (like the heat coming off a hot road) and may bubble. This is normal.
- Allow the pH reducer to do its work for 20 - 30 minutes, then turn on the pump and circulate the water for at least 4-6 hours.
- Test again after 48 hours and repeat as necessary.
1 gallon = 3.8 litres
1kg = 2.2 pounds
1 litre = 34 ounces
After giving the pool an "acid shock" like this, it is usual for the pH to drop. The high Total Alk causes the pH to rise again naturally, so wait several days after correcting the TA before adjusting the pH up. It is usually not necessary after the wait.
There are some who suggest that this method can harm some pool surfaces and they warn not to add more than 2.5 pounds of pH reducer for 10,000 gallons of pool water every 3-4 days. I regularly use up to 20 pounds for 10,000 gallons in one go and I have yet to have a problem. As long as the hardness level is at least 200ppm there is no reason for problems.
Comments and suggestions are welcome.