New pebblecrete pool - PH issues and brown staining

[dylk]

Hi all,

Found this great website and have been reading a fair bit. I have made some assumptions on what I need to do here but hopefully someone can assist.

See images. Pool is only a few months old, PH rises constantly up around 9 and then ill bring it back down once a week. There was some waste from pebblecrete construction in the filter so I have assumed PH problems are from this ‘fresh’ pebblecrete. I have replaced this filter. For reference, I have dumped probably 15L hydrochloric acid in over a few months. PH usually rises back up over a few days.

Furthermore over time the white pebblecrete seems to be getting brown spots /splotches all over the pooland brown areas around edges. Wall brush does not remove. It’s not terrible but seems to be slowly getting worse. Note the pebblecrete had no brown in it.

Would I be correct that getting the PH down and keeping it a bit lower than recommended ~6.5 might alleviate this problem?

Thanks in advance.

 

[ajw22]

Welcome to TFP.

How do you chlorinate your pool?

How do you test your water chemistry?

Can you tell us the water chemistry from your test kit in the format:

FC
CC
pG
TA
CH
CYA

It is helpful to know details of your pool and equipment. Please create your signature with those details.

 

[dylk]

Hi thanks for the quick reply.

Signature updated

I had a water test conpleted. May be easier to read it in the image attached. I have since lowered the PH to around 7.2 (for now).

My discussion with the pool shop was they weren’t sure why this was happening but dont bother correcting anything until PH is stable. Chlorine is low I assume due to water chemistry being out. Pool runs for 8 hours a day.

Thanks

31000L (8.2K gal), IG concrete/pebblecrete, Viron XT S2 pump, Astral XC100 cartridge filter, Astral E series Saltwater Chlorinator (Magnesium additive)

 

[ajw22]

I suspect your brown spots are algae.

You are too focused on your pH when your pool needs chlorine.

I suggest you review...

Pool Care Basics Archives

Your one-stop shop for all things TFP to include: ABCs of Water Chemistry, Recommended Chemicals/Levels, Test Kits, Troubleshooting, and much more!

www.troublefreepool.com

And get your own test kit from Clear Choice Labs.

With their test kit you can do a Overnight Chlorine Loss Test and then follow our SLAM Process to clear your algae problem.

@mgtfp @AUSpool can help you more about testing and chemicals available in your country.

 

[dylk]

Thanks @ajw22 for the quick response.

I will do so and see how I go. Needed the nudge in the right direction!

 

[ajw22]

What Are My Ideal Pool Levels?

Use our tool to find ideal chemical levels for any swimming pool. Check TFP recommended levels on pH, free chlorine, cyanuric acid, and more.

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The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

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Recommended Pool Chemicals

Which should I buy? TFP's recommended pool chemicals are cheap, easy, and won't unbalance your pool water.

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SLAM - Shock Level and Maintain

We’ve all had to deal with a green pool. Clear algae from your pool with a SLAM! Read here to use shock level and maintain to clear your pool.

www.troublefreepool.com

 

[mgtfp]

Welcome to TFP, mate!

Yes, get a test kit from Clear Choices Labs.

Those pool shop results look suspicious. A pH of 9 sounds a bit unlikely, and that CH of 17ppm also looks a bit dodgy. What's the CH of your fill water? Do you use softened water? Bore water?

I also suspect algae, but you could try rubbing a vitamin C tablet on the spots. If that removes them, then they would be iron stains.

 

[AUSpool]

Geday and welcome,

Yamba is such a lovely corner of the world, lucky you.

Firstly never go below a pH of 7. A pH of 9 would be a big red flag the shop should have discussed with you, some thing is wrong there.

Your pH will always move, get on top of the free chlorine, FC, asap. I would add about 500ml of pool chlorine to start and work on getting a decent FAS/DPD FC test.

Unfortunately self testing for calcium is going to be difficult with the magnesium in there.

I hope the brown is just algae but iron is a known contaminant of the magnesium salts and iron stains can be brown. Was the salt brushed around until fully dissolved? And then brushed again after about 6 hours with the pump running the entire time?

 

[AUSpool]

Have you actually added any magnesium salt or is the chlorinated just suitable for magnesium?

What was used to bring you salt up to 4800ppm?

 

[mgtfp]

Good catch, @AUSpool, I missed that magnesium. If you actually added magnesium salt, then the magnesium content might be too high to be suppressed with the Taylor or Clear Choice Labs CH test. You might do better with the Red Sea Calcium test for aquariums, that is better at dealing with interference from higher magnesium levels. It uses different units (ppm Ca instead of ppm CaCO3), but that can be converted, we can help you work that out should you decide to go down that road.

I'd recommend to switch to sodium chloride, aka plain old salt, for your future salt top ups. Magnesium is bit of a hype in Australia these days. But the only thing it actually does is help improving the revenue if the companies selling it.

The Astral E series is specified to work in a wide salt range, 4000-8000ppm. Your salt level is spot on (if that salt measurement is correct), that recommended range in the printout of 3000-4000 is wrong for that chlorinator.

 

[dylk]

Thanks everyone for the input. I will work on the chlorine side first. Glad I added that little snippet about magnesium! Cheers for taking the time to notice.

The pool builder added magnesium at the beginning i.e. a few months ago. From memory, some liquid additive and replaced one bag of salt with magnesium chloride (or similar). When i got it tested a month or so later, salt was low, so I added plain salt. It was brushed around extensively at the time but possibly not enough I guess. Was a bit weird on hard brushing the fresh pebble early on...

Sounds like I should try the vitamin C test as well? Probably worth noting the brown spot is visible on essentially all horizontal surfaces.

 

[AUSpool]

I had been thinking that there is something wrong with that total hardness, TH, test result. Our tap water supply normally has around 100ppm of TH so that result of 17ppm just can’t be right. I’m not very confident in those store results. Plus now we know you have added magnesium that hardness result is even more sus. I guess there’s not much choice in Yamba though. You really need to know what your calcium hardness is for a concrete pool and get it up to at lest 250ppm. Indicating hardness is a bit old school where they just assume magnesium is negligible and hardness = calcium but for some reason magnesium has become a big thing in Australia. With the power of advertising everyone thinks they want it. If you get water tested you need to tell them you have magnesium and ask them to use an 801 disk in their spiny thing. You need separate results for magnesium, calcium and salt.

 

[mgtfp]

I don't think the low reading is because of Magnesium, I think that's just dodgy in it's own way. It's more that at high Mg levels the Taylor buffer solution can't remove all the Mg anymore before starting the titration and it would partly show up in the CH test.

Have a read through this thread here:

Taylor CH, Salt tests and Magnesium Chloride

My pool has a high level of Magnesium Chloride in the salt mix (popular in these parts with SWG for the supposed therapeutic benefits of Mg). I was wondering if this might be throwing out a couple of the Taylor tests. 1. CH is reading very high, 900ppm on a new pool with no additives other than...

www.troublefreepool.com

That was a case where high Mg levels lead to a false high CH reading, also in Australia. Matt did some explaining in that thread and recommended to try an aquarium test kit for CH. The OP then tried the Red Sea test kit and that seemed to have done the trick.

 

[AUSpool]

Agreed, the low hardness test at 17ppm is just dodgy. It’s a store test result, could be Taylor but I suspect a Lamotte spin disk. Tap water has more hardness then 17ppm and with the magnesium in there it should be much higher.

@dylk Have you put any calcium chloride in to raise your Calcium hardness? I would go ahead and test with the vitaminC, the cheapest one from coles or Woolies. But we hope it’s just algae in which case a slam will fix that. If that 20ppm of CyA can be trusted you would wont to raise it up to 30ppm. In 31kL 310g will raise your CyA by 10ppm. This just helps prevent loosing a bunch of your FC to UV break down.

 

[dylk]

Cheers for continued replies. Sounds like my best bet is to find someone who can do a test for metals.

However testing has not come back with any useful results. Spot tests with chlorine, 15x 500mg asorbic acid tablets crushed and held for 5 minutes yielded no changes. After yesterdays discussion I shocked the pool (before your suggestion above unfortunately) and that had no result this far. It may even look worse.

Our tap water is not filtered and is dirty, could this be dirt that has firmly settled in , not to mention all the sand that blew in their after construction which i was vacuuming out regularly. Someone else in the area told me they pressure wash their pebble!

Yes after my initial pool test I added i think from memory 1-2kg of calcium which apparently had no effect.

 

[mgtfp]

If it hasn't reacted to vitamin C, then it's not iron.

I'd order the CCL test kit asap and then do an Overnight Chlorine Loss Test to give us a baseline.

We are not big friends of the one-off shock dose. Algae needs high chlorine levels maintained until it's all dead, see SLAM Process. To follow that process, you need the FAS-DPD chlorine test that's in the CCL kit.

Your shock dose making it rather worse than better might just be that that was a drop on a hot rock, and algae still keeps growing. Or that there are other metals (we only ruled out iron) that got oxidised by the chlorine. Could there be copper in the water? Either from filling the pool or adding products containing copper?

Until your kit arrives, I'd add 5ppm worth of liquid chlorine daily, you can calculate the required amount with PoolMath.

 

[AUSpool]

5ppm/day of bleach i 31kL‘s is 1300ml/day @ ~12%. My 500ml initial dose estimate was way too low.

Have you added any algacides?

 

[dylk]

Hi sorry for the delay.

No i have not, would that be a good way while i wait for the kit to see if algae is what I am dealing with?

5ppm/day of bleach i 31kL‘s is 1300ml/day @ ~12%. My 500ml initial dose estimate was way too low.

Have you added any algacides?

 

[mgtfp]

No, it's good that you didn't add algaecides. We asked about them because they often contain copper which can eventually cause metal staining.

Chlorine is all you need to get rid of algae and to keep it away. But it is important to understand that the FC level needs to be adjusted to the CYA level, as most of the chlorine binds to CYA where it is UV protected, but useless as a sanitizer.

You need an FC level of 40% of the CYA level (for example FC 20ppm for CYA 50ppm) to clear an algae infested pool. And then maintain a level around 10% of the CYA to keep it algae free. That's what the recommended FC/CYA Levels are about