Recommendations sought to balance pool chemistry

[DIYconvert]

I'm a new pool owner that bought a house with an old pool. The plaster is degraded and coming off in chunks. I was told it is a 37,000 gallon pool; however I have not calculated the volume myself yet. It is kind of kidney shaped with a deep end around 10-11 feet. The water was green when we moved in so we hired a pool guy to fix it up. He came by several times a week (cleaning, chemicals, and filter maintenance). After a month I got a $500+ bill and decided I needed to do this myself!

The pool is fairly clear; however there is some green algae on the sides. It's been raining a lot; however none for the last three days. The pool guy was here 5-6 days ago and loaded up the floater and the skimmers with 3" tabs. The water level has been consistently dropping so I've been running a hose into the pool 3-4 hours a week to keep the water level above the bottom of the skimmer inlets. I hope I don’t have a leak. I plan to do the bucket test ASAP. The filter has been running 12 hours/day (8 am to 8 pm on timers).

I read through some of the forums, tried out some of the calculators, and bought my TP100 test kit. Yesterday, I bought some chemicals at the grocery store; however I just guessed what I might need because I hadn’t had a chance to test the pool yet. I got the following:

6.5 gallons 6% bleach
12 lbs baking soda
4lbs Borax

I came home and tested with the following results:

FC .5
CC .5
TC 1
pH < 6.8 (Is there anyway to get a more accurate pH reading using the TP100?)
TA 10
CH 430
CYA 20

Based on what I read in the forums and my interpretation of the calculators I decided I needed to shock the pool with bleach with a target FC of 15. I calculated I needed 9 gal of bleach so I just put everything I had in the pool (6.5 gal of 6%) and turned on the filter. This morning I retested with the following results:

FC 16.5
CC .5
TC 17
pH < 6.8
TA 20
CH (did not retest)
CYA (did not retest)

I know I need to get my pH and TA up. Should I use a combination of baking soda for the TA and borax for the pH or just washing soda? Won’t the washing soda take care of both? What order should I take?

I don’t know my pH; only that it is less than 6.8 since that is all the test kit can tell me.
However, according to the pool calculator I should:

Add 694 oz by weight or 554 oz by volume of baking soda to go from a TA of 20 to 100
and
Add 153 oz by weight or 134 oz by volume of washing soda or soda ash
or
add 305 oz by weight or 293 oz by volume of borax to go from a pH of 6.6 to 7.5.

I appreciate any recommendations.

Thanks, Chris

 

[duraleigh]

Hi, Chris,

Get the Borax into your pool pretty quickly. You need to get your pH up in the 7's and, since the test only goes to 6.8, it's hard to tell how low it is. Calculate to go from 6.8 to 7.4 (that'll be a bunch of borax) then check your pH a few hours after you put it in (in the skimmer, pump running) and add more if necessary.

Hold off on the baking soda 'til your pH comes up in the 7.2 - 7.8 range. That'll bring your Alk up as well and then you can calculate and add baking soda to get into the 80 - 120 range

You might need some more chlorine pretty soon. If the algae is still present after today, kick the Cl back up into that 15+ range and hold it up there until the algae is gone.

Couple of other things to talk about but I'd really like to see you get the pH up in a satisfactory range first.

BTW, no other test for pH is available that doesn't cost a ton of money. You'll get more used to that color matching as you use it more often.

You have a good working knowledge of what's occuring in your pool. The plaster is probably not salvageable but it's not doing short-term harm....sounds like you can live with it for a while.

Washing soda is a scarce item here in NC....borax and baking soda are readily available.

 

[DIYconvert]

Thanks for the info, Dave. I told my wife to dump the one 4lb box of borax into the pool already. I need about two more boxes per your suggestion. I'll pick up 4 more on my way home along with some more bleach and test again before I do anything.

When is the pool swimable? I assume the FC and pH have to be in the normal tolerance range before anyone can go in.

 

[duraleigh]

Once the pH got in the 7's, I would be comfortable swimming in that pool.

Others are a little more cautious about higher chlorine levels.....I have never experienced any issues being in a pool that was @ 20ppm.

The pH below 6.8, however, might eat the buckle off your new swim trunks and create an awkard moment!! :lol: :lol: :lol:

 

[DIYconvert]

About 4 hours after the 4lb box of borax I got home and tested with the following results:
FC 6.5
CC.5
TC 7
pH <6.8
TA (did not test)

I was planning to add only two more 4lb boxes but I calculated that I still needed 3 to get the pH from 6.8 to 7.4 so that’s what I did. The algae is still around so I decided to shock again and added 4.5 gal of 6% bleach as well. I then brushed the pool to loosen up some of the algae. Four hours later I just retested with the following results:

FC 14.5
CC .5
TC 15
pH 8.2 (The top of the graduated color scale; might it be even higher but still match the color for 8.2?)
TA 40

The borax worked too well. I think my pool volume is wrong. When I asked the pool guy he estimated it to be 34,000; however he seemed to have just said that number off the top of his head. Maybe not. It might just be that the pH swung so far because my TA is still too low. I have about a gallon of muriatic acid that I found in the storage shed. I don’t know how old it is. Based on 34,000 gallons, to move my pH from 8.2 to 7.6 I should add 90 oz of acid.

Should I add the acid? If so, can you confirm the amount I need to add? It’s late so I’ll check the pH again in the morning before I do anything.

Thanks, Chris

 

[Guest]

do NOT add the acid. High chlorine levels will cause the pH test to give a false high reading. Wait until your FC levels drop below 10 ppm before trying to adjust the pH. It is very likely your pH is NOT as high as you think it is right now.

 

[DIYconvert]

Thanks, waterbear. I didn't add any acid. I retested the pH this morning and it had already dropped to 7.8. The FC is still >>5 of course. By this afternoon, after several hours of sun, I'm certain the pH will be in the optimum range of 7.4-7.6. I think I'm on my way to a "trouble free pool" and my daughter and her friends can swim in it now! Thanks to everyone who helped me; including chem geek (Richard) who got me started with all this. I'm not done yet, though. I need to get my TA and CYA up and, eventually, get my FC down when the algae is finished off. It's looking better already.

What are my next steps?

 

[JasonLion]

What waterbear said, plus unless you are using Richards PoolEquations spreadsheet (not for novices) you shouldn't trust the calculators for PH changes when your TA is that low. Low TA lets the PH change more easily, so you need less chemical to change it, sometimes dramatically less. Likewise high TA would mean you need more chemical to change the PH.

You need to get your TA up a bit and you can work on that while shocking the pool though it would be best if you don't add bleach for a few hours after adding baking soda. I would try 6 lbs of baking soda for now. Then you can bring TA up a little more once you get the PH balanced.

 

[DIYconvert]

I think I'm getting it; however I'd like some reassurance.

Based on JasonLion's suggestion, I added 6 lbs of baking soda two different times. Each time my TA went up by about 20. Here are the current readings:

FC 4.5
CC .5
TC 5
pH 7.2
TA 70-80 (The solution started turning red on the seventh drop and the 8th one made it bright red. Should I count the reading as 70 or 80?)

The algae on the sides has definitely gotten better. However, because its an old pool and the plaster is in bad condition I'm not sure what is algae vs. old stains. Can I ever expect to have a consistently white pool surface? The FC has been steadily dropping from its last shock high of 14.5. I presume that I must still have some organics that are using up the FCs.

Before I started the baking soda, the pH went down to 7.2 and has been holding there for the past 24 hrs. The baking soda is working to get my TA up; however it's not raising the pH any.

Here's my plan:

1. I need to shock again and keep the FC up around 15 until I see that it doesn't go down overnight.

2. Concurrently with the shocking I will keep working on the TA by adding baking soda incrementally until I get the TA up to around 100. I probably only need one more 6 lbs treatment.

3. Once I get the TA where I need it, if the pH hasn't gone up anymore I plan on adding some Borax to get the pH to 7.4-7.6.

4. I presume my CYA hasn't changed from my initial reading of 20 because what I've been working on shouldn't have affected the CYA in the pool. Once I'm done shocking, my TA is in a good range, and my pH is holding steady I will test my CYA again. To get the CYA up to the 30-70 range I will have to actually go to the pool store and get a stabilizer.

I appreciate any comments; especially on my bolded questions and any incorrect assumptions I may be making.

Thanks, Chris

 

[Buggsw]

You should go with the 8th drop. When you test, you add drops until the color doesn't change any more. So for instance, probably a 9th drop wouldn't have changed the color any more, so you would count it as 8.

Baking soda affects TA more than pH. When TA is really low, the baking soda will affect the pH more than it will if your TA is getting to optimal readings - so what you are seeing is normal - and good.

 

[DIYconvert]

Should I add stabilizer now to help keep the FC from getting used up? Or should I wait until I'm not shocking anymore? The stabilizer instructions say I should start with the FC at 1-4 ppm. However, it also says the optimum CYA range is 20-25.

I started working the plan above yesterday; however I didn't have enough chemicals so I just used what I had. After adding four 96oz jugs of 6% bleach and one 4 lbs. box of baking soda my numbers looked like this at the end of the day:

FC 5
CC .5
TC 5.5
pH 7.3-7.4
TA 80

The FC level probably went up some after adding the bleach in the morning; however it was mostly used up by the end of the day. The little bit of baking soda raised the pH some but didn't do much to the TA.

Today, I went and got some more chemicals, including one 4 lbs container of hth stabilizer. I tested first with the following results:

FC 2
CC .5
TC 2.5
pH 7.3
TA 80
CYA <20 (I filled the view tube to the top and could still barely make out the black dot)

The FC continues to drop. I decided I needed to take care of the chlorine first so I just added three 192 oz. jugs of 6% bleach. I think I'm going to need more than 4 lbs of stabilizer. Restating my question: When can I add the stabilizer?

 

[duraleigh]

Hi, Chris,

I see you're working on several issues at once...your pool chemistry and some problems with your equipment.

I'm gonna' respond to your chemistry issues and suggest that your understanding of your equipment will come around and not to dwell on that 'til your chemistry is correct. As long as you're circulating the water, get your chemistry in line and then take those equipment issues one at a time......

So, add your stabilizer any time you want but keep in mind it may take several days for it to register correctly when you do the CYA test. Using Jason's calculator (and knowing how many gallons are in your pool) you should easily be able to add the correct amount to bring you up to your target range. Then, be patient....you can't test for it right away. Just have confidence you have calculated it correctly.

Next, How does your water look? Any sign of algae? If so, bring your FC up this evening into the 15ppm range to shock your pool. Hold that FC up there, day and night, until your pool water is clear. If it's clear already, just keep your FC around 2-5ppm constantly (the Sun will get a lot of it each day) for the rest of the season.

Let your pH and Alk stabilize for the next day or so. You're very close to being perfect on those so I'd suggest leaving tham alone for now and focusing on the correct amount of stabilizer and keeping chlorine in the pool.

Tuesday or Wednesday, you can retest all your numbers and post 'em up. You'll probably have some minor adjustments and be good to go.

In the meantime, you can get familiar with your equipment. What's puzzling to you now will become quite clear if you'll address each issue one at a time and your pool will be Trouble Free.