SWCG may be causing chemistry problems?

[Heavyhook]

I posted the info Whizbang Spinner requested a week ago but haven't had a response at this point. We have just gone through a very busy holiday weekend and I know folks have a lot going on in their lives besides this forum. If their is another PF Support Team that would care to give me some guidance on my current problem I would be very grateful. Thanks!

[chem geek]

Your high TA is the primary cause for your fast pH rise and at higher pH and TA you are probably getting calcium carbonate scaling in your SWCG cell in spite of the low CH. At pH 8.0, the saturation index is +0.2. The borates help to reduce the problem, but are not enough given your high TA. The good news is that you have no overnight chlorine loss which means you don't have anything consuming chlorine in your pool like algae or organics.

Test your tap water to see the TA and if it's a lot lower then the pool then some water replacement will help, but you can also accelerate the lowering of TA by following the "add acid and aerate at low pH" procedure described the Lowering Swimming Pool Alkalinity -- A Step by Step Guide. It's going to take a lot of acid to get your TA down -- every gallon of full-strength Muriatic Acid (31.45% Hydrochloric Acid) will lower your TA by 40 ppm but you won't add these all at once. You follow the procedure to lower the pH to around 7.0 and keep it there while aerating.

[Heavyhook]

I have aerating 24 hours round the clock form a strong jet from my filter return aimed at the surface. My tap water test are PH 8+, CH 10ppm, TA 260ppm. Our water is supplied from local wells. Our bedrock is limestone not far below the surface. At 7:30 am this morning water test were FC 3.5ppm, CC 0 ppm, PH 8.0 , Acid demand 5 drops to 7.6 ph, TA 100ppm, CH 60ppm, added 121 oz's 8.25% bleach.
My TA & CH are dropping as you anticipated. My scaling on the liner has been reduced by 75% so far. I have been adding 32 oz's of 31.45% Muriatic Acid daily. If I understand the Lowering Swimming Pool Alkalinity -- A Step by Step Guide correctly my PH needs to come down to 7.0 then be allowed to rise to its natural level. When should I start to see the PH drop? Do I need to increase the volume of Muriatic Acid daily since the TA has reached the target level of 100ppm to get the PH to drop now? Do I need to stop aerating ? Am I assuming right that I stay on bleach with SWCG off until all the water chemistry numbers are where we want them?
Also I looked back in my notes to 3 years ago when I changed the water in my pool. I had added 16 pounds of Calcium before I found the PoolForum and discovered it was not necessary with a vinyl liner pool!

[BigDave]

Since you have a SWCG, you might go a little lower with the TA.

Adding the Acid will bring the pH down directly (TA too). The aerating is to bring the pH up (without increasing TA) after reducing it with acid; when your pH and TA are where you want them, stop aerating.

You can always use bleach for chlorination. When you do resume operating the SWCG, pH will probably start to rise - use acid to keep it where you want it.

[Heavyhook]

Chem Geek recommended aerating and following directions from Pool Doc in "Lowering Swimming Pool Alkalinity -- A Step by Step Guide" which includes the following,


"If your CA / TA level is not what you need to be, then you keep adding acid, so the pH will stay down:
. . . so the lost carbonic acid will keep being replaced with newly converted carbonic acid
. . . so the CO2 will keep gassing off
. . . so the CA will keep dropping.

When your CA gets where you want it, just stop adding acid, but keep aerating till the pH returns to the 'normal' level.

Ben
PoolDoc"

My PH levels have never dropped during the time I have been reducing the TA and CH levels. This may be where I am getting off track. Pool Doc and Chem Geek say to keep aerating, and my understanding was that doing so during SWCG operation would help GAS OFF the CO2 created by the electrolysis process to help prevent the PH rising. Don't at some point I need to add enough acid to drop my PH to near the lowest level of my test kit recommended in "Lowering Swimming Pool Alkalinity -- A Step by Step Guide" ?

[kelemvor]

Yes, you need to be adding acid and testing pH often to keep the pH low while you aerate. Only when you're done do you need to let the pH rise back up.

The more often you can manage to test and adjust, the better it will likely go.

Something else worth mentioning. You can increase the CYA to 60ppm and reduce some of the chlorine loss due to sunlight. In Texas, it probably beats down just like it does for me here in FL. The circupool user guide recommends 30-60 CYA - I'd go 60. Also, the 7ppm fc is a little high of a target with a swcg. You really only need to be between 1-3. Lowering the output on your swcg to target this range will help keep pH climb in check too.

[BigDave]

Since you've reached your TA goal without ever getting the pH into the low end, finishing the TA reduction process will be a little different for your pool. Stop aerating and add acid until your pH is where you want it.