Constant pH and chlorine battle

[tadcpht]

So this is the first full year of the BBB method. Pool has been crystal clear all year, no complaints there. I test the water about every other day. The pH always reads 8.0 or higher and the chlorine reads low or non existent. I add clorox bleach to get the chlorine up between 3-5ppm and muriatic acid to bring the pH down to 7.4. I am having to do this every other day. Is this normal? Alkalinity ranges between 70-100ppm if it is low then I add baking soda to bring up. Right now my numbers are as follows:
pH 8.0
FC 0.5-0.0
Alk 100
CYA 60

I added clorox and muriatic acid to remedy the pH and the FC. Is there something I can add to help the FC stay longer and the pH stay down? I had a CYA problem (well above 100) last year and had to drain 3/4 of my pool and refill so I have been very cautious about adding any tri-chlor tabs or shock. Thanks!

 

[Patrick_B]

Hi tadcpht,

I would encourage you to stop adjusting your TA. Leave it alone and lower you pH when you hit 8.0 as you have been. I assume by your sig that you don't have a SWG or water features? Pools tend to rise in pH, some more than others.

Your FC is very low, what's going on with that?

 

[jblizzle]

You should be adding bleach EVERY day to maintain the FC above the minimum based on your CYA level. The FC is lost to the sun and to organics ... you have to replenish it every day.

CYA is what protects the FC from sun and makes is last longer. Your CYA is already slightly above the recommended levels, so you should not raise it more.

Odds are that if the FC has gotten too low repeatedly, you should go through the SLAM process ... or at least do the OCLT to see if there is anything in the water.

 

[duraleigh]

The pH is what it is. You need to continually add acid to keep it below 8.0 regardless of how much it takes. I would also suggest leaving your TA alone for now. What is the pH of your fill water?

If you are bringing your FC up every other day from it's near zero now up to between "3-5" ppm, then that is normal loss. Most pools lose 2-3 ppm daily.

More correctly, you should never let your FC get below about 4-5 ppm and if you are only adding every other day, then you need to add about 4-6 ppm MORE to compensate for the loss.

 

[tadcpht]

No SWG. No water features. Just did a FAS/DPD drop test. After I added the clorox about an hour ago.
FC 4.5
CC <0.5

Does my FC need to be higher?

So after reading the replies I think I need to bring the FC up to around 10ppm? and not let it go below 4-5. I was under the impression that to swim, FC needed to be between 3-5ppm. Also are the SLAM and OCLT procedures somewhere? not sure how to do those. Also should I ever add any algaecide? I have not put any in this year. Thanks again.

 

[jblizzle]

Algaecide should never be needed ... assuming you are maintaining adequate FC.

Have you read any of Pool School?

With a CYA of 60ppm, the FC should never be below 5ppm, so you should dose up to around 8ppm everyday to ensure it does not drop below 5ppm: pool-school/chlorine_cya_chart_shock

Here are links to the SLAM Process and Performing the Overnight Chlorine Loss Test

 

[tadcpht]

Yes, I did read pool school a few times. There is a lot of info there to remember. Thanks for the links. If I keep it between 5-10ppm is there a need for the OCLT and SLAM tests? Obviously I have been running the FC too low.

 

[jblizzle]

Maybe.

IF there is anything growing in the pool (pretty likely given past FC numbers), then you need to SLAM. You can do the OCLT to determine if there is something in the pool. I would suggest raising the FC up to at least 10ppm when you do the OCLT.

 

[Smykowski]

I was under the impression that to swim, FC needed to be between 3-5ppm.

Where did you see this? If it's leftover pool store info, please brain dump it quickly. I promise you'll be much better off.

 

[massimo]

 

[chem geek]

As Dave says, just focus on keeping the pH lower, but do two things. First, the TA will drop over time but do not increase it by adding baking soda. Let it drop. When it gets to 70 ppm or so, see if you notice the rate of pH rise and the amount of acid you need to add being less than before. Also, when lowering the pH don't lower it below 7.5.

The general rule is that if the pH tends to rise you do NOT want to raise the TA. In your case with a vinyl pool you can have the TA be low without issues. If the pH becomes more stable at a much lower TA, then that's fine. Worst case, if you have to get to 50 ppm TA for stable pH then you can use 50 ppm Borates for additional pH buffering, but let's see how you do when it's at 70 ppm TA.

 

[chessie6]

Just a couple pennies from me . . my TA needs to be around 30 in order for the PH to stop rising. There's always a rise of PH right after the bleach is added which goes down the next day, so I test PH the next day (I add bleach in the late afternoons).