Pool alkalinity and PH?

Question

We just got our inground pool installed (IntelliChlor Salt Chlorinator, pentair pump, sand filter, vinyl) and I'm totally mixed up. Our most recent water test results show the following:

Total Chlorine 0.5

Free Chlorine 0

PH 8.3

Total Alkalinity 296

Adj. Total Alkalinity 284

Total Hardness 278

Minerals 3200

Borates 7

I shocked the pool with the appropriate function on the IntelliChlor Salt Chlorinator and increased output to 80%.

The pool store gave me both sodium carbonate and sodium bisulfate as well as Lithium Hypochlorite to boost the chlorine level.

There is still a bit of hardscape construction and landscaping going on around the pool (so plenty of dust, dirt and sand flying around). The pool water (which originated as well water) is cloudy and dirty looking.

Shouldn't I be adding hydrochloric/muriatic acid and sodium bisulphate to reduce total alkalinity.

Well ... what should I be doing? Please ... your expert help would be very much appreciated. Thanks

Answer 1

Sorry Bob but recent research has debunked the "slugging" method. This is very dangerous for you liner. The area you decide to slug can be weakened by the decreased pH in that area. Especially in vinyl. Unfortunately you are another victim of the pool store. Lithium hypochlorite is the most expensive form of chlorine on the market. I would suggest using it until you run out then using regular unscented 6% clorox bleach. It is much cheaper. Bleach contains the same active ingredient as chlorinating liquid (sodium chloride) only chlorinating liquid is 12%. They say sodium bisulfate is used to drop only the pH while muriatic acid is used to drop the TA. They BOTH drop pH and TA (even using the slugging method).  The safest method to drop the TA is using muriatic acid to lower the pH to 7.0-7.2 (which will also lower the TA) then aerating the water to bring the pH back up and repeating the process until your TA is inline. When you create bubbles in your pool (aeration) it releases carbon dioxide. As the carbon dioxide leaves your pool the pH will rise. In 20000 gallons 3/4 of a gallon of 31.45% muriatic acid will lower you pH to 7.2 and bring your TA down 19ppm. Then aerate your water until the pH reaches 7.8 and repeat the process. When the pH is 7.8 1/2 a gallon of acid will lower it to 7.1 and bring your TA down 13ppm more. A note on salt water generators (SWG). The SWG will aerate the pool for you. When it creates chlorine tiny bubbles form which is why these pools usually have a high pH. This process should be fairly easy to accomplish.

Some advice (I service about 20 of these pools)- get your TA to 60-80ppm to help fight the pH rise you will be constantly battling. Get your CYA level to 80ppm. This will make the chlorine last longer. I would suggest not using the SWG to shock as all this does is put the setting to 100%. The higher you set it the shorter the life span of your cell.

Here is how a SWG works. They usually run on either a 15 min or 30 min cycle. If you set the dial to 50% it will create chlorine for 7min 30 sec or 15min (depending on your cycle). Set at 10% it will run for 1min 30sec or 3min (again depends on the cycle).

High TA can contribute to cloudiness but more than likely it is your 0 FC. Get your chlorine up to shock level by adding 3 1/2 gallons of 6% bleach (will bring FC to 11ppm in 20000 gallons). Slowly pour the bleach into the pool in front of a return so it mixes properly. Leave your filter running 24hrs/day until the pool clears. You need a good test kit to know your FC level. You should keep the FC at 11ppm until the level holds overnight. This ensures all organics in the pool are dead. Watch your filter pressure. When it raises 15ppm higher than normal backwash. Getting your chlorine up will help clear the water. If you have any more questions feel free to email me.

Answer 2

Yes, you need to drop the TA. It ought to be in the 80-120 range. You use muriatic acid to do this by what's called "slugging". Pick a spot in the deep end, away from a return and skimmer and make sure that your main drain suction ( if equipped) is turned off. Add the appropriate amount of acid in that spot. Re test in 24 hours or so. You don't give a pool volume so I can't recommend an acid amount, but what I usually do with a pool that needs the TA dropped and it's an unfamiliar pool, is to add no more than 1.5 L of acid during the slug and see what the result is. Not all pools react as planned and doing it with this small amount won't take you below 80 TA but will give you an idea of the amount of change for the 1.5 L ( That's approximately 1/4 of a jug if this is an American pool :) )

TA is pretty well the most important aspect of pool water chemistry since it acts like a governor on a car engine. If it's in the right range, not only do all other chemicals work better but it also reduces wild swings in other parameters, like pH.

Your salt level is up isn't it? I'm not familiar with your particular unit, but almost all of them like to be in the 2500- 3200 ppm range to work properly. Your pool temperature needs to be up as well. They don't tend to generate much chlorine if your pool water is 70 F or below.

You'll need to keep the unit dialled up as well. That construction you have going on is dumping a lot of organics in the pool and that in turn is using up free chlorine.

Edit:

Sorry Muss. but years of pool pros doing it this way and actual research has shown it to be the best way to lower TA. It in no way endangers a liner since it's dilute at the bottom. If you'd like to argue the point, consult Dr.Neil Lowry's research on the matter. You have taken one of his courses haven't you? If not, you're a little late, but you may find some of his research papers online.I also installed and serviced over 100 of these salt water pools on a weekly or bi weekly basis so...if it's a numbers game to you Muss, fine, but that's not what matters in the long run.

Answer 3

Hey Muss:

How do you figure bleach 6% is cheaper than pool chlorine?  I pay $2.50 per gallon of 12.5% and that would mean a gallon of chlorox should be $1.25???  Not in my store!

You're welcome!!