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High Ph requiring 14 oz of Dry Acid to get water in range


Forgiven1

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Just wondering why I can't dump in all 14 oz at a time.  I am pulling an all nighter to do the 0.8 oz every 30 minutes that's required.   Also, because it's taking so long do I need to worry about bacteria building up in the water?  I currently have no sanitizer in the water because I have read the ph needs to be balanced before sanitizer can be added.  The employee at the pool store said that was a bad Idea to wait.   Can't seem to get the same answer from any place I look.   

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You will need to supply some details on your situation before anyone here can assist.   What size is your tub? What are your current water chemistry values (i.e. TA, pH, CH)?  What are you using for sanitizer?

It is true that sanitizers do their best work in a fairly narrow pH range, but that does not mean they don't work at all outside that range.  I would maintain a normal sanitizer level while you are doing your balancing. 

If you have not already seen it, there is a sticky in this forum on lowering your TA and pH effectively.  You do not want try large changes like that all at once.  You also don't need to stay up all night to do it.  Have a look at the sticky and post your test results and answers to the questions above. Here is a link to the process:

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/ 

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Thanks for the response.  I have a 415 gallon hot tub that I just filled.  All the literature I read said to adjust for ph BEFORE adding anything else.   After having put in about 1/2 cup of Dry acid (.8oz at a time while jets were on for 30 minutes) I didn't see a difference at least when I checked by test strips.  A day later I Took a sample of water into Leslie's and here were the results after the 1/2 cup of acid

 

Ph 8.6

TA 205

 

The recommendation was to add 14.5 oz of dry acid to get the ph within appropriate levels.  Using the directions on the bottle, that would take about 9 hours which I have to split over 2 days, Meanwhile with no sanitizer in the water this whole time.  My concern is bacteria forming while I try and balance the ph.  Also, I heated the hot tub to 90 degrees as it was recommended for the dissolving of chemicals most effectively but I know that can also cause a breeding ground for bacteria as well.  

That's why I was wondering since the test tells me I need 14.5 ounces of acid, why I can't just put it all in at once.  I keep seeing that it's not safe but I'm just wondering what exactly would that level do?  Does it harm the tub?  Does it give off fumes that are toxic?  Will my tub explode?....😱

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Did your calculations call for 14.5 oz dry acid by weight or by volume?  If it was 14.5 oz by weight, that would convert to around 9.5 oz by volume.  If you've only added a half cup (4 oz by volume), then you aren't even half way to 9.5 oz yet.  So, at this point, your total alkalinity may have dropped somewhat...but your ph is still going to be rising back up fairly quickly (the higher the total alkalinity the faster the ph rise).  Until you are done adding the necessary amount of dry acid, the ph will only be lowered for a short time after you add the dry acid and then it will quickly be rising back up...it is only after the total necessary amount of dry acid has been added that the ph will begin to stabilize.

I would double check whether you needed 14.5 oz by weight or by volume.  It could very well be either...it just depends on your water source.  In my case, for a similar sized tub, I actually need around 16 oz by volume (which would be around 24 oz by weight).

As far as adding the acid, you want to do it incrementally...but you can safely add slightly larger increments in the beginning.
If you actually need only the 9.5 oz by volume (14.5 oz by weight), then I would do something like this:

Add 3 oz dry acid (by volume), then let the pumps circulate 30 minutes...
Then, add 2 oz dry acid, then let the pumps circulate another 30 minutes...
Then, add another 2 oz, and let the pump circulate 45 minutes...
Then, add 1.5 oz, and let the pump circulate  another 45 minutes...
Then, add 1 oz, and let the pump circulate for an hour...

At this point you will have added the 9.5 oz total.  If your total alkalinity isn't testing below 100 at that point, you probably need a little more dry acid...your target total alkalinity may vary a little bit, but 70-80 is what I shoot for.

You definitely don't want to add the entire necessary amount of dry acid all at once, but if you are providing those periods of aeration by running the jets in between doses then you can get the total amount needed added (in an incremental fashion similar to how I described) and have it all done in a few hours. 

As far as the reason it is unsafe to add the total amount of dry acid all at once...the ph would actually drop too low...this would mean that it would be unsafe for you or anybody else to get into the tub, and it would be corrosive to your hot tub equipment...

The total alkalinity AND the PH of the water are both lowered by adding dry acid.  However, aeration (running the jets for a period of time) will raise the PH without raising the total alkalinity.  So, gradual incremental additions of the acid coupled with periods of aeration will allow the total alkalinity to be lowered without running into the problem of lowering the PH too dramatically.  Once the total alkalinity has been lowered to the target range, the ph should remain fairly stable.  It will still be necessary to add small amounts of acid periodically, but the ph rise will have slowed to the point that you may only need to add a maintenance dose of dry acid (perhaps 1 to 2 tablespoons) once or twice a week.  If you are using Dichlor or some other sanitizer that is acidic, you may need even less frequent maintenance doses of dry acid.

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