Second Pool Season Woes – Can’t Remove What Looks Like Sand

[reaganmarine]

First of all I’d like to say this site is fantastic. As of last year I’m a new pool owner and I have found the site to be invaluable during all phases of pool planning, construction and maintenance.

The construction for our concrete 18 X 36 pool began late in the fall of 2013 and it opened in May 2014. Now that we’re into our second season we’ve discovered some spots on the floor of the pool that resemble brown and black sand. The pool has a standard white plaster finish. The surface of the plaster underwater is noticeably less smooth as compared to the plaster just above the waterline. There is also some modest amounts of marks on the floor of the pool that (the company that company that opened the pool) referred to as crocodile skin.

I brought the situation to the attention of my pool builder and he said he believed the pool had a bit of calcium build up. He suggested adding 10 gallons of acid, turning off the equipment for 3 to 4 days and to brush for 3-4 times a day. He said that should break that calcium up. He said that once it feels smooth I could add alkalinity increaser to balance the water again. He suggested having the water professionally tested afterward. He also said this problem could have been caused by high PH over the winter (we closed our pool in early November of last year). He forewarned me of this so (as he suggested) I pulled back the cover in mid-January and added one gallon of acid then brushed the entire pool for 30 minutes. I had hoped to repeat this process but never made the time to do so. Last season, during the beginning of the curing process, I was very good about checking the PH every week and adding acid as needed in order to keep the PH from skyrocketing (I’m happy to say the PH fluctuation has finally slowed down here of late).

I’d truly appreciate a second opinion on this problem before I make such a drastic change. I should add that our children (of course) have already been in the (very cold) pool for several swims this year but have not complained of a rough pool surface. I’ve been very diligent with the pool testing (last year and this year) using the TF-100 test kit which has been extremely helpful. Below I’ve included an underwater photo of the problem and some recent test results. Thank you!



5/18/15
FC 4.5
PH 7.8
TA 50
CH 400
CYA 50
Salt 3800

4/24/15
FC 6.5
PH 7.2
Salt 2800

4/17/15 (pool opening)
FC 0.5
CYA 70
Salt 2600

12/27/14 (before adding acid)
PH > 8.2

8/27/14 (towards the end of last season)
FC 4.0
PH 8.2
TA 80
CH 325
CYA 50
Salt 3200

 

[kimkats]

What happens when you brush it? Have you tried putting a chlorine puck on it to see what happens?

I don't know about what your PB wants you do to. What kind of warranty do you have with him?

Kim

 

[reaganmarine]

Thanks for the reply. It doesn't move when you brush it and I haven't tried a chlorine puck. The pool has a typical full warranty that's why I ran everything past my builder first in case I have to call on the plaster company's warranty.

 

[reaganmarine]

I went ahead and added the acid as recommended and I also have tried the puck test. The acid was added yesterday afternoon. We brushed three times afterward without any change. The brushing continued today without any change. I placed a chlorine puck on one of the spots today too. I checked it after 30 minutes and after 1 1/2 hours but it had no affect on the stain. I updated my builder late yesterday and he said it would take some time for the acid to work. He also said I could accelerate the process by adding an additional 3-4 gallons of acid (10 gallons have already been added). Since the pump is off should I be adding liquid chlorine to keep up the FC? The equipment will be off for 3-4 days so I'm concerned other problems will develop during this time. Any other thoughts on the stains?

 

[kimkats]

I am all out of ideas I don't know what to tell you. I would be worried about the pump not running BUT you have to do what the PB says.

Let us know what happens.

Kim

 

[reaganmarine]

Can anyone suggest how much alkalinity increaser I should have ready when it's time to reopen the pool. I tested the TA last night and the sample wouldn't turn green during the initial steps (it turned red). I think I only have 5 lbs. on hand; leftover from last season.

 

[chem geek]

If it turned red immediately then that implies not only 0 ppm TA but a pH of 4.5. Check the pH and if it's truly low then immediately increase it. How did the pH get so low and the TA used up? That usually only happens when people use Trichlor and don't monitor the TA or pH so the TA drops over time and the pH then crashes. Hopefully you haven't damaged your equipment with the low pH.

 

[pooldv]

I went ahead and added the acid as recommended and I also have tried the puck test. The acid was added yesterday afternoon. We brushed three times afterward without any change. The brushing continued today without any change. I placed a chlorine puck on one of the spots today too. I checked it after 30 minutes and after 1 1/2 hours but it had no affect on the stain. I updated my builder late yesterday and he said it would take some time for the acid to work. He also said I could accelerate the process by adding an additional 3-4 gallons of acid (10 gallons have already been added). Since the pump is off should I be adding liquid chlorine to keep up the FC? The equipment will be off for 3-4 days so I'm concerned other problems will develop during this time. Any other thoughts on the stains?

You added 10 gallons of muriatic acid to your pool? No wonder you have no TA or PH. This could be a BIG problem. Do NOT add more acid. I am going to PM for help.

 

[Patrick_B]

Ok, don't turn on the pump yet. You don't want that going through your heater if you have one. Nor your SWG. If this is done, you'll need to bring up the pH with Soda Ash until it's high 6 pH range. Soda ash, not baking soda (Aka Alkalinity increaser) You need to begin adding and mixing manually with a brush thoroughly by brushing the pool until you get a pH of at least 6.8. Then circulate with the pump and add in small amounts. Test an hour after each addition until you reach a mid 7 pH 7.4-7.5. Stop there, let it rest, and re check pH a little later to double check where you are. How long did PB tell you to acid bath the pool? How long you wish to try this is up to you, but he is trying to have you dissolve the Stains/deposits with the acid. Sometimes it works, sometimes not. Either way, it isn't good for the plaster.

 

[reaganmarine]

You added 10 gallons of muriatic acid to your pool? No wonder you have no TA or PH. This could be a BIG problem. Do NOT add more acid. I am going to PM for help.

pooldv - Thanks for the reply but my inbox is empty. ?

- - - Updated - - -

Ok, don't turn on the pump yet. You don't want that going through your heater if you have one. Nor your SWG. If this is done, you'll need to bring up the pH with Soda Ash until it's high 6 pH range. Soda ash, not baking soda (Aka Alkalinity increaser) You need to begin adding and mixing manually with a brush thoroughly by brushing the pool until you get a pH of at least 6.8. Then circulate with the pump and add in small amounts. Test an hour after each addition until you reach a mid 7 pH 7.4-7.5. Stop there, let it rest, and re check pH a little later to double check where you are. How long did PB tell you to acid bath the pool? How long you wish to try this is up to you, but he is trying to have you dissolve the Stains/deposits with the acid. Sometimes it works, sometimes not. Either way, it isn't good for the plaster.

Patrick B - Thanks for the reply. The PB said give it 3-4 days. Why soda ash and not baking soda? (just curious) What kind of harm might this cause to the plaster

 

[Patrick_B]

Plaster base is made largely of Marble, which is Calcium more or less and Acid dissolves Calcium. The damage caused by it just shortens the life of the plaster. To what degree I can't say, but it will. Doing too many of these over the life of the plaster will shorten it's life expectancy significantly. That will lead to pitting, cracking, and general decay.

You don't want to use Baking Soda because once you reach a certain pH, say about 7.2, you see a lot of TA increase without getting much more pH increase. Once you get the pH I suggested, you'll have enough TA to work with and you can then tweak that level if you need too. And you likely may in this case. Just curious, what did the PB give you as a neutralizing procedure once this is done?

 

[reaganmarine]

Patrick B - Thanks for clearing that (baking soda) up. The only step the PB mentioned was to add alkalinity increaser (after 3-4 days) to bring the water back to balance and to have the water professionally tested. Are there other steps I need to take before I turn the pool equipment back on?