UK Indoor Pool Refurbishment

[jakeblat]

Found a few tablets for CH in the Lovibond 5 in 1 set and got a result of ~240. It's a slightly difficult test to get an accurate read on because you keep adding pool water to the re-agent until it quite suddenly changes from violet to pink.

I've added 1.6 litres of hydrochloric acid which I had left over from last year to get started on lowering the TA. I don't know how to convert the concentration to correspond with the muratic acid options in the Pool Math app, the product I used (Blue Horizons TA Reducer) states it contains hydrochloric acid 20%

 

[PoolStored]

I've added 1.6 litres of hydrochloric acid which I had left over from last year to get started on lowering the TA. I don't know how to convert the concentration to correspond with the muratic acid options in the Pool Math app, the product I used (Blue Horizons TA Reducer) states it contains hydrochloric acid 20%

Multiply 1.6 litre by 2/3 to get 1067mL, then use 1067mL with the 31.45% entry in pool math.

 

[mgtfp]

I missed that Hardness reading. But that really is Hardness, it matches the Calcium reading, just in different units, it's not Alkalinity. The difference between the Calcium and the Hardness is, apart from the different units, that one is Calcium Hardness, and the other Total Hardness, which would also include other types of Hardness like from Magnesium. That both values match once translated into the same units shows that your Hardness is mainly only Calcium Hardness. But the Calcium test is the one that we are actually interested in, but it requires above explained unit transformation.

It's a bit confusing that TA and CH are both using the same unit CaCO3, but they are different things. One quantifies the amount of CaCO3 one had to add to get the same amount of Ca²⁺ into the water as the test found, and the other quantifies the amount of CaCO3 that would add the equivalent amount of CO3^2- that would give the same Alkalinity reading.

So, the Alkalinity in that report really has to be read as 505 ppm in pool units, and your PoolLab reading is far off from that. I'm not opposed to the PoolLab in general, but the TA test really doesn't cut the mustard, I have tried it a number of times. Sometimes, it accidentally kind of matched my Taylor test (when I say "kind of" then I mean that I wanted it to match, but it actually didn't), but most of the time it was wildly off. And with a dilution to get TA above 500 into the PoolLab range of 200 max there is an additional test error.

TA management will be critical for you with such hard fill water with both, high TA and high CH. I'd really recommend to find a proper titration test for TA and CH. You need a reliable test. See what you find for Aquariums, post it here and we can discuss whether it looks suitable and how to translate the units of the test into pool units.

 

[jakeblat]

Does this look suitable for testing CH? https://www.amazon.co.uk/Salifert-8714079130347-Calcium-Test-Kit/dp/B001EIZT4Y

It looks like a titration test and claims to offer a resolution of 10ppm per drop.

 

[jakeblat]

I also found this titration based alkalinity test which might be suitable. Looks like I'd also need the dechlorinating reagent too.

Alkalinity (P), (M) and (OH) Testing Kit | Boilers | Cooling | Closed System | Feedwater Website

Buy Alkalinity Titration Kits at Feedwater for testing Alk M, Alk P and Alk OH by the method of dropper titration

feedwater.co.uk

 

[mgtfp]

Both those tests should work.

The calcium test will give you ppm Ca, which you will have to multiply with 100/40=2.5 to get ppm CaCo3.

For the Alkalinity test, you'll only have to order the titrant and the 4.5 Indicator which is for Total Alkalinity which they call Alkalinity (P) in their test. The colour change of the other indicator for Alkalinity (M) is above pH 8 anyway, and this type of Alkalinity is pretty much zero at pool pH. (I just edited that, I had written Alkalinity (P) twice, but the second has to be (M)).

This test will give you the correct units in ppm CaCO3. Use a sample size of 40ml which will give you a resolution of 10ppm. While your TA is above 200ppm, you can also use a sample size of 20ml to get 20ppm resolution which will save you some reagent until your TA has been reduced a bit.

Also order the dechlorinating reagent they are mentioning with a link.

 

[mgtfp]

Loving your project by the way. Great effort.

 

[mgtfp]

The Alkalinity test instructions say to add 10 drops of dechlorinating reagent, independent of the sample size being used, so I assume it must be enough even for an 80ml sample. For a 40ml sample, 5 drops should definitely be enough. You'll see if it's not enough when the indicator bleaches out and doesn't give either not the expected starting colour or the correct colour change at the titration endpoint.

 

[jakeblat]

@mgtfp Thanks for the advice. I've just got the Salifert Calcium test and repeated it twice. Result was 110 ppm which x2.5 = 275ppm CaCo3

Going to be a while before I get hold of the alkalinity test, that feedwater site does sell just the Alkalinity (P) version so I'll order that along with the dechlorinating agent. Looks like they're not shipping anything out until after Christmas now though so will probably be a couple weeks.

 

[mgtfp]

Good. That seems to match your water report. If the report is also correct about TA and it is around 500, then your CSI would be probably between 0.3 and 0.4 thanks to the colder water. That's not too bad for now, but once you get to 25°C-30°C, CSI would be above 0.6, which would result in scaling sooner or later.

Wait for your TA test, then you'll still have enough time to get your TA down before the water starts warming up. In the meantime, just keep managing your pH.

Another indicator is that 1000ml of half strength acid only brought your pH from 7.4 down to 7.3, which is in line with a TA of more like 500 than 240. But there was a day between adding acid and the next TA test, so pH could have risen during that day.

I'd say, once pH is above 7.8, dose acid to get you down to maybe 7.4. Ideally test again after about 30 min with the pump running. Use 240 for now as TA for acid addition calculations, you don't want to overdose. PoolMath will tell you to add about 1.2l to get pH from 7.8 to 7.4 with TA 240. I suspect, it will get pH only down to 7.6.

I wouldn't go for large pH reductions (like more then 0.4) in one step, to avoid getting accidentally too low. Add acid, test after 30min, then add more and retest after another 30min.

Each 1 litre addition of half strength acid will reduce your TA by about 10 (you can calculate that in the effects of adding section of PoolMath - but don't trust the pH calculation in the effects of adding, it doesn't consider the actual TA value there).

Once you have your TA test and actively start reducing TA following these instructions

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

then you might want some ventilation in your pool enclosure to blow outgassing CO2 (which is heavier than air) away from the pool surface.

 

[jakeblat]

Finally making some progress again after everything has been on pause for the cold weather.

I've got the titration test kit for Alkalinity (https://feedwater.co.uk/wp-content/uploads/2014/07/Alkalinity-Titration.pdf) and tested my water. Result is 240ppm. I used a 20ml sample, added 0 drops of titrant after adding the Phenolphthalein Indicator to give a result of ALK(P) = 0. I then added the 4.5 indicator and added 12/13 drops to get the colour change to yellow/light orange.

At this stage should I continue to try to lower the total alkalinity using muriatic/hydrochloric acid additions, then aeration to bring the ph back up? I don't fully understand if this process will work when it appears the water hardness appears to be the only contributor to the high TA?

Separate from water chemistry I've been making some progress cleaning the pool surround and getting ready to repair the sections of the rubber flooring that were lifted during the repair. All the floor is getting power washed and rinsed to lift out all the construction dust/debris and the windows/brickwork washed down.



Where sections of the floor are damaged I'm getting ready to repair them by gluing down an sections that are still in good condition then using a wet pour rubber surface repair kit to fill in any gaps or areas where I can't re-use the cut out sections such as around the skimmer. Sadly I couldn't get an identical colour formulation for a reasonable price so I've gone with something that looks similar. Next year I might look at redoing the surround properly but I just want to cover the concrete and get the floor level for now.



The rubber granules and resin for the repair.



I've got a repair to do on the ladder where someone replaced a bolt but didn't use the appropriate stainless steel type.



And lastly I've got the skimmer and 1 return plumbed in to the pump and filter. There's still another return to get trenched in and connected but I need to cut out and remove a small concrete slab first. The flexible hose on the drain setup it temporary until I can get some 1.5" to 50mm adapters to connect to the existing white drain pipe on the bottom right. The heat pump is currently disconnected as I'm going to pour a new concrete pad for it to sit on. I'll cut the return line from the filter to get it connected up once the temperature improves. Just as I finished this work some more cold weather has arrived so I've drained everything down again.



Also located alongside the pump and filter are the new electrics. The pump and heatpump each have a Shelly Plus 2PM relay with power monitoring which are connected to my home automation system (Home Assistant). The light transformer is in the box at the back left and also has a Shelly for control of the pool light transformer. I've also replaced the outdoor lights with new smart lights in the background and will also be replacing the internal lightning with smart lights soon. In my attempt to make all the things "smart" the motorised ceiling window openers are also now connected to a Shelly Plus 2 for positional control. Once the weather warms I'll be starting a project to make the older heat pump smart and add wifi control to it. My plan is to eventually automatically divert excess electricity production from my solar panels to the heat pump rather than exporting it back to the grid for a low price.

Frustratingly as I completed all the pipework and electrics I found the mortar was crumbling in the equipment enclosure and most of the top layers of brickwork were loose. I'll be following up on this later and redoing the brickwork and making a new more weather resistant lid as well.

 

[mgtfp]

At this stage should I continue to try to lower the total alkalinity using muriatic/hydrochloric acid additions, then aeration to bring the ph back up? I don't fully understand if this process will work when it appears the water hardness appears to be the only contributor to the high TA?

Even though Hardness (CH) and TA are both measured in the unit ppm CaCO3, they are still different things.

Having a CH of 100ppm means you have the same amount of CA++ ions in the water as you would get from adding 100mg of CaCO3 to 1l of water and dissolving into the water as Ca++ and CO3-- (Carbonate) ions. That doesn't necessarily mean that the Ca-- ions got into your water by adding calcium carbonate, it's just an equivalent.

In the same way a TA of 100ppm means that you have the same TA in the water as you would get from adding 100mg of CaCO3 to 1l of water and dissolving into the water as Ca++ and CO3--. Here it's basically giving the equivalent amount of Carbonate ions (CO3--) creating the same TA as you have in the water.

Depending on the pH, some of the CO3-- (which has a double contribution to TA because of the two charges) will change into HCO3- (which has only a single contribution to TA, but because in the process one H+ got consumed, which has a negative contribution to TA, the net TA is unaffected) and into H2CO3 (which has no contribution to TA, but the process removed another H+). The H2CO3 actually splits mostly up into CO2 (which drives CO2 outgassing) and water (H2O).

Then, in a pool, there is also a contribution of CYA to TA. But all of these TA contributions are basically measured as an equivalent amount of added CaCO3 that would yield the same TA in the form of CO3--.

To calculate the Calcite Saturation Index (CSI), which tells us if water is scaling (CSI>0) or aggressive to plaster surfaces (CSI<0), we are interested in the amount of CO3-- in the water, which can be calculated from TA considering pH and CYA.

When both, the amount of CO3-- and Ca++, is too high (technically it's the product of the two), then the water is "oversaturated", and some Ca++ and CO3-- will form CaCO3 and fall out of solution as scale. If the product of the two is too small, then the water is undersaturated with CaCO3 and can draw some Calcium out of plaster surfaces to reach saturation.

Therefore, you don't want both CH and TA high. Someone with low CH can afford higher TA in terms of CSI.

But independent from CSI, high TA always drives pH drifting upwards by CO2 outgassing. That's why we recommend to maintain lower TA to slow down pH drifting up.

That was a lot of stuff, hope I didn't overwhelm you with that...

 

[mgtfp]

I should add that in your case with a vinyl liner, low CSI is not really a concern for you, but high CSI can be. But as long as you keep TA in TFP's recommend range, and CH is not above the ideal range, CSI will be of not much concern for you. You certainly don't have to worry about low CH. There should never be a reason for you add calcium increaser.

Keep in mind that by replacing evaporation losses with fill water, CH keeps accumulating.

You want TA low enough that with Summer water temperatures and pH around 7.8 CSI is below 0.3 to avoid scaling. Play around with PoolMath a bit.

Also, once you have your TA below about 70-80 (maybe a bit lower in your case because there is less of a CYA contribution to TA, therefore more Carbonate in the water as in someone's pool with the same TA but higher CYA), pH rise usually slows down, and you can maintain a fairly constant pH around 7.8, with not many acid additions (adding acid only once pH hits 8). Important for allowing pH up to 8 is that there is some CYA in the water even in an indoor pool, otherwise you can't neglect the pH effect on the effectiveness of chlorine. And of course that TA and CH are low enough to not create a scaling problem.

Just don't let TA drop below 50ppm.

 

[Newdude]

That was a lot of stuff, hope I didn't overwhelm you with that...

I'm not too proud to say it......




WELL done as always.

 

[jakeblat]

Well it took some additional reading but I think I now understand the chemistry of how the acid works to lower the total alkalinity. I've got another 15 litres of Blue Horizons TA Reducer (20% hydrochloric acid) and have been repeating the acid addition and waiting for the ph to come back up with aeration. I've added 4 litres so far and my TA is now down to 170 (using the titration test), so I'll keep on going until I'm just under 100.

The CSI calculator in the app is proving useful for me to understand the kind of ranges of ph/temp/alkalinity that will cause me trouble, especially once I get the heatpump going again and get the temperature higher. There was definitely an issue with scaling before I started this refurbishment as the ladder is still covered in it where the waterline was, so I'd like to avoid any scale build up in the future.

I've got one other thing to look at which is excess air in the top of the filter. Using the manual bleed on top only seems to push out water, not air. I have a suspicion there's some air getting in on the suction side through the unions as there's a very small stream of bubbles in the pump filter basket. I'll take out all the union and pump o-rings to check them when I've got a chance and see if I get any improvement. I don't actually see any bubbles coming through the return in the pool though even though the filter has an auto air vent tube that just touches the underside of the clear lid

 

[mgtfp]

Looks like you're getting on top of TA now, good job.

Leaks can be annoying to find. There are some tips in this article, see if that helps:

Suction Side Air Leaks

If you see air bubbles coming out of the return lines in your pool, you likely have a leak. Some signs that a suction side plumbing leak has occurred include: Read more

www.troublefreepool.com

It's great to see the progress with your pool, what a great project that you've taken on.

 

[jakeblat]

Suction leak turned out to just be some dirt on the o-rings for the pump / valve, took them out and cleaned them and the mating surfaces, put some lube on the o-rings and the pump basket is clear of bubbles now

 

[jakeblat]

Now the weather has improved I'm finally getting the pool up to temperature ready for use. Have been doing a few of the remaining jobs in the meantime like filling in and tidying up the trenches for the pipework, and repairing some of the pool surround.

It would have been expensive to get a colour match on the rubber flooring colour so I decided to just go contrasting. I plan to redo the surround in a year or two and just need something functional for now.



The material is a shredded rubber that's mixed with a polyurethane binder. I only needed a small quantity so mixed in a bag, tipped onto the concrete then troweled smooth.



Finished result, not perfect but the material is easy enough to patch / touch up. It's really clear the existing rubber is quite old and has suffered quite a bit of UV fading.



I've been putting off dealing with the last of the pipework trenches for weeks because my backfill material around the pipes needed to be carried up ~30 steps.



About half a tonne of gravel was used to backfill then as much dug out chalk and dirt compacted over the top as possible. Because carrying all that gravel wasn't difficult enough I ordered another tonne of decorative gravel to cover the area after putting down a weed membrane, helpfully the place I bought it bagged it into 25kg bags that could be moved more easily than the loose material I'd previously ordered.



Not sure if this will be the long term solution, I might pave the area in the future or have a small deck and add handrails to stop anyone falling off the retaining wall.

Lastly I've been heating the pool with the heatpump when the sun is out but may have been a bit ambitious doing it in April, overnight temperatures are still getting down to 4C (40F) and it being enclosed but unheated only provides some protection.

The green line below is from manual temperature measurements during the day, orange line is from a wireless temperature sensor in the pool. I've only really run the heatpump during the day ~9-5 so you can see the rises in the day and drop overnight



More detail for those who like graphs. Pool temperature on left axis, other temperatures on secondary right axis. W/m2.mea is measure of solar irradiance, W.mean is power consumption of the pump + heatpump, ws_temperature_2 is air temp in the pool house.

 

[mgtfp]

Great progress, awesome work!

 

[jakeblat]

Should also mention that my test results are looking very close to where they should be now. I continued the acid addition process and my TA is now down to ~110 from >250 (checked with titration test, and PoolLab now closely agrees - was way off when it was high). pH has been very stable for weeks now when previously it had been rising steadily.

FC 1.8 (may increase this slightly once the pool is in active use depending on how fast it falls / if I increase CYA)
CC 0.1
pH 7.5
TA 110
CYA 10 (waiting to see whether this needs to increase once the pool is in-use and uncovered as I don't know how much UV gets filtered out by the windows/glazing)
CH 240

I was checking I had all the pieces to put the ladder back in and annoyingly it looks like the cover plates for the pinch anchors got thrown away at some point during the refurb, have ordered some new ones as well as new rubber feet/caps to go on the ladder as the existing one's seem to be a bit perished. Also already replaced a rusty steel bolt on the ladder with an appropriate stainless bolt and made sure all the tread bolts were tightened properly - ladder feels nice and stiff now.