Water keeps getting saltier and possibly damaging pool surface

[Trentlane]

Hi everybody,
Firstly, apologies if this is better suited to a different forum it just seems a little out of the ordinary so thought I'd try the pool chemistry wizard types.

I recently bought a house with a pool and moved in 5 weeks ago. As far as i know it is an old school chlorine pool. It is painted concrete. There is no chlorinator and i didn't think it was a salt water.

When we moved in the pH and alkalinity were crazy high. Particularly the alkalinity. I can't remember exactly what the readings were but both beyond the scope of my home test kit. When I took it into a local shop the kid was very surprised. After about 2 weeks of adding 500ml Hydrochloric acid each day i finally got them both pretty good. But then, the trouble started. Two separate leaks in the pipes connected to the filter. The water started getting really salty tasting and leaves white salty deposits where ever its splashed. Sediment kept collecting on the bottom of the pool within 24 hours of vacuuming. Pretty sure it was coming straight through the filter. When I left it on the bottom of the pool for a few days there were stains left behind. Also getting stains (or possibly paint coming off) in other spots. If i scrub at them with a brush most of them almost come off completely but not quite. Some are just solid stains - look almost like rust stains.


The sediment situation has gotten much better after vacuuming it to waste. But each day there is still some new stains on the paint.


Unfortunately, I don't have a salt reading for when I initially moved in and the pH and alkalinity were really high. Shortly after that (about 2.5 weeks ago) the reading was 8300 ppm and then a few days ago it was up to 11800ppm. This is based on the sample I brought to the local pool store.

My only working theory is that because of the high pH and alkalinity the filter and/or pipes were filled with mineral deposits, scale etc and when i got the chemical balance more neutral they started breaking down causing the leaks and maybe the saltiness. Just to clarify, I haven't added any salt. I have added only hydrochloric acid, stabilised granular chlorine, "pool sunscreen", and one of those blue gel cubes for clarifying since moving in 5 weeks ago.


I think I am going to have to get a submersible pump and drain or partially drain the pool to get the salt level down. Am worried its doing damage to the surface. But also a bit concerned about the structural problems that could arise from draining the pool.

Any input is appreciated.

The filter looks quite old, I have backwashed and rinsed several times. The little plastic "window" for checking that i have backwashed enough is completely yellowed so can't see the water unfortunately.

I had set some money aside for getting an electric heat pump but definitely need to get everything else sorted first. I anticipate getting a new filter and pump and chlorinator. But also considering alternative sanitising methods.

 

[mknauss]

Welcome to the forum!
Are the readings you show salinity or TDS? Very different things.
Salt would only increase if you added it. At the low levels you show, it will all be dissolved.
I suggest you read ABC's of Pool Water Chemistry.

 

[Trentlane]

Welcome to the forum!
Are the readings you show salinity or TDS? Very different things.
Salt would only increase if you added it. At the low levels you show, it will all be dissolved.
I suggest you read ABC's of Pool Water Chemistry.

Thanks for the response.
Regarding salinity vs TDS, unfortunately, I can't seem to find the printout to check if there was anything definitive on there but at least now I know what to look for. I googled salinity vs TDS.

I do get that the idea is that "salt" should only increase if its added (or when water evaporates but prior to topping up with fresh water). But short of someone sneaking into my yard when I am not around and dumping salt in my pool that isn't what has happened. Which is why I am trying to think outside the box. As far as the actual test readings go, it's always possible one or both of these were inaccurate for some reason. But that doesn't explain why there are now two leaks in the pipes attached to the filter. Nor why it feels and tastes salty. Nor the white salty looking deposits on the pavers and glass anywhere that gets splashed. And the most pressing issue to me is all the marks and/or paint coming away from the surface that wasn't happening earlier.

I recall from High School days that there are lots of different types of "salts" even though in day to day life we are usually referring to Sodium Chloride. Not sure if calcium or any other mineral deposits that could of accumulated in the pipes would come into play.

Regarding seeing the salt, the water itself looks clear. It's not that i think I can see it floating in the water. It's just that I am concerned the high levels are doing damage.

The other thing I am considering is that there is probably a lot of air getting in to the water. As when the pump is off, air is getting sucked into the pipes and filter area through the leaks.

Thanks for the suggestion regarding the ABC's of pool chemistry. I have read it - re-read a few bits. I think it's a great intro but didn't really go into salinity vs TDS, or effects of too much salt etc.

Thanks again for your response. Let me know if you have any other thoughts.

Andrew.

 

[BenB]

The next step is getting yourself one of the "real" test kits that we recommend here, as pool store trying can be wildly inaccurate. I recommend the TF-100 as you get lots more reagents for your money, but I'll be honest I don't know if it's available internationally. You will also need a Taylor 1766 salt test as again without it we don't really know what the numbers are for sure.

 

[proavia]

Being in Australia, your only option for a good test kit is to contact Clear Choice Labs. They offer a test kit that is close to the TF-100 and/or K2006C. You should also ask about a salt test when you contact them.

Chances are no one here will make recommendations based on pool store results as we have seen they are highly inaccurrate.

 

[Trentlane]

The next step is getting yourself one of the "real" test kits that we recommend here, as pool store trying can be wildly inaccurate. I recommend the TF-100 as you get lots more reagents for your money, but I'll be honest I don't know if it's available internationally. You will also need a Taylor 1766 salt test as again without it we don't really know what the numbers are for sure.

Thanks

 

[Trentlane]

Being in Australia, your only option for a good test kit is to contact Clear Choice Labs. They offer a test kit that is close to the TF-100 and/or K2006C. You should also ask about a salt test when you contact them.

Chances are no one here will make recommendations based on pool store results as we have seen they are highly inaccurrate.

Thanks. I was actually looking at their test kits online last night. Thanks for the recommendation.

I was a little put off when i realised that iffff my last salt reading from the pool shop was even slightly close to correct it will take me about 60 drops of titrating reagent.

 

[kellyfair]

Thanks. I was actually looking at their test kits online last night. Thanks for the recommendation.

I was a little put off when i realised that iffff my last salt reading from the pool shop was even slightly close to correct it will take me about 60 drops of titrating reagent.

Since no one has added salt to this pool, that test result is very suspect. At any rate, the first step to getting pool chemistry under control is to run the tests yourself.

What is the strength of the muriatic acid that you used? You were adding 500ml every day for more than 2 weeks? What were your ph and TA readings, and was this also pool store testing?

Also, I’m no metric system guru, but isn’t 18kl around 4800 gallons? That is a really small pool... someone please check my math!

 

[needsajet]

Welcome to TFP! Good to have you here

For your first salt test, you could dilute the pool sample (e.g. 250 ml pool water, 750 ml distilled water) and then multiply drops by 800 (instead of 200).

Yep, 18000 litres is 4800 US gallons, and yep that would be plunge pool size. Maybe let us know the surface dimensions and shallow end / deep end depths so we'll know.

Sadly, yeh, we can't do much with pool store test results. The two wildly different readings for salt, which changes verrry slowly in a pool, is a good example of why.

With the kit, you'll be able to take full control of the water and with help from here at TFP, you'll be able to solve most everything, and at a lower cost than with pool store potions.

 

[Trentlane]

Since no one has added salt to this G, that test result is very suspect. At any rate, the first step to getting pool chemistry under control is to run the tests yourself.

What is the strength of the muriatic acid that you used? You were adding 500ml every day for more than 2 weeks? What were your ph and TA readings, and was this also pool store testing?

Also, I’m no metric system guru, but isn’t 18kl around 4800 gallons? That is a really small pool... someone please check my math!

The acid strength is 380g/l.

Prior to adding acid:
pH 8.2 from store test and about 8.4 on home test kit (not a fancy one). Currently sitting at about 7.4 - test strips.
TA 234ppm store test and about 250 ppm home test kit. Currently about 120.

Sorry. The 18kl is a typo. My estimate based on dimensions is that it's about 38 kl. Roughly 10000 gallons.

Thanks for the reply.

 

[Trentlane]

Welcome to TFP! Good to have you here

For your first salt test, you could dilute the pool sample (e.g. 250 ml pool water, 750 ml distilled water) and then multiply drops by 800 (instead of 200).

Yep, 18000 litres is 4800 US gallons, and yep that would be plunge pool size. Maybe let us know the surface dimensions and shallow end / deep end depths so we'll know.

Sadly, yeh, we can't do much with pool store test results. The two wildly different readings for salt, which changes verrry slowly in a pool, is a good example of why.

With the kit, you'll be able to take full control of the water and with help from here at TFP, you'll be able to solve most everything, and at a lower cost thawith pool store potions.

Thanks.

I really like your dilution idea. I never would of thought of it. Will do it as soon as the kit arrives.

 

[Trentlane]

Here's my latest "Where did my mysterious salt come from conspiracy theory backyard chemistry" idea - provided by a helpful person on another (non-pool related) forum:

HCl (hydrochloric acid) + NaHCO3 (Buffer) = NaCl (salt) + CO2 + H2O

Don't get me wrong I didn't actually add any sodium carbonate myself but perhaps if there was a lot of it in solution already?????

I don't know. I guess it doesn't really matter where it came from so long as i can get rid of it and it doesn't come back.

 

[needsajet]

Many of the pool chems add a little salt, and over time it can rise if there's little splashout or water removed due to backwashing, but best we wait until you have your own kit and reliable results.

In the meantime, add 1 litre of liquid pool chlorine per day just to keep it from changing. Avoid any further additions of stabiliser or chlorine powder or tablets. Your kit will include a test for stabiliser (aka cyanuric acid, aka CYA) and it will be interesting to see the result for CYA.

Liquid chlorine comes in the 15 litre returnable blue jugs. When full, they're a bit heavy and prone to causing splashes. You can set the full jug partly in the pool water to take some of the weight, and then tip the liquid into the pool water. An estimate of 1 litre is fine for now. The jugs pour more cleanly/easily when they get down to around 11 or 12 litres.

 

[mgtfp]

Here's my latest "Where did my mysterious salt come from conspiracy theory backyard chemistry" idea - provided by a helpful person on another (non-pool related) forum:

HCl (hydrochloric acid) + NaHCO3 (Buffer) = NaCl (salt) + CO2 + H2O

Don't get me wrong I didn't actually add any sodium carbonate myself but perhaps if there was a lot of it in solution already?????

I don't know. I guess it doesn't really matter where it came from so long as i can get rid of it and it doesn't come back.

You don't have to look for complicated reactions to find NaCl being created, that separates in water anyway into Na⁺ and Cl^- (Chloride).

A salt test only tests for Chloride, doesn't matter where that Chloride comes from, could be from "normal" salt (NaCl) or Calcium Chloride (CaCl₂ - which is what the pool shop calls Calcium Increaser) or Hydrochloric Acid (HCl) or actual Chlorine that ends up as Chloride after it;s done its job killing stuff or being destroyed by UV (a tiny bit more Chloride when the Chlorine was added as Liquid Chlorine, as that contains some lye as well). Or even Magnesium Salt (MgCl₂) - maybe the previous owner added some fancy "Mineral Salts" because he enjoyed having a real salt water pool?

If you added for example 5l of Hydrochloric Acid (please don't do that in one go...), then your salt would probably rise by something like 70ppm - there is an effect, but nowhere near what you appear to have seen.

Was there really a noticeable change in how salty the water tasted? Or does the water simply taste salty now, but you never tried it before? I could imagine that the salt level was high to start with, the differences between 8000 and 12000 ppm are probably just testing errors anyway, I don't think the pool store tests are designed for these levels (they are questionable to start with...).

I'm not quite sure if I understand the issue off "Two separate leaks in the pipes connected to the filter." correctly. What exactly are you describing there? What's the intended function of these pipes? Have they always been filled with water, or sitting empty for longer periods?

 

[AUSpool]

Use a bit of caution with the salt test, it can cause nasty stains. Use gloves and put plastic down, don’t do it anywhere near good kitchen benches or tables etc.

Excessive salt is not the cause of the broken pipes, you need to look at getting those pipes fixed, that’s just as important as getting pool balanced. Pressure pipe is not to hard to work with is your handy.

 

[YippeeSkippy]

I'm kinda concerned about the pool having been painted instead of re-plastered? Paint rarely lasts any more and some sellers seem to want to cover up things with it. Could you be seeing paint chips on the pool floor?
High calcium levels can also spew white chips at times, say from a salt water chlorine cell. Do you have one?
Did the last owners leave any chemicals behind or instructions?

Maddie

 

[AUSpool]

Painted pool surfaces on plaster are not as uncommon as you might think, with both acrylic and epoxy paints. It was a common finish prior to pebblecrete.

@Trentlane The best way to lower TA is by reducing pH to 7.0 or 7.2. Just putting in 500ml of acid every second day is not a good approach. Acid is added slowly in front of a return. I dilute mine first. I hope you didn’t tip it in the skimmer, that could cause equipment damage including leaks. Have a look at this article about reducing TA.

Lower Total Alkalinity - Trouble Free Pool

 

[AUSpool]

The filter looks quite old, I have backwashed and rinsed several times. The little plastic "window" for checking that i have backwashed enough is completely yellowed so can't see the water unfortunately.

I had set some money aside for getting an electric heat pump but definitely need to get everything else sorted first. I anticipate getting a new filter and pump and chlorinator. But also considering alternative sanitising methods.

Don’t be tempted to backwash to often, a mechanical filter preforms better as it gets dirty. You need to find your pressure gauge and make sure its working. You take a baseline pressure reading after backwashing and then only backwash when it gets to your baseline pressure + 25%.

Electric heaters are expensive to install and the running costs are up there. My sparky said he has pulled out more than he’s installed. I’ve had solar and will have one again. Well suited to our climate.