Paper dip tests record different results to tablet tests

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I have an outdoor splasher pool of circa 10'000 litres and I hope someone can explain why my PH test kits are registering wildly different readings.

I use phenol red tablets in a lovibond style tester to ascertain PH levels are within acceptable bounds. I've always maintained this at 7.2 or as close as I can get it to that which matches our tap water reading. I have bought several test paper kits for the purpose of testing CYA, the last was Blue Horizons branded. All have shown the pool to be too acidic, while the tap water is shown as 7.2. So, something in the pool is clearly reacting with the chemical in the test paper in a different way to how the chemical in the tablets does. The pool doesn't seem to burn my skin when swimming, so I don't think it is acidic, but it's highly annoying that the readings cannot be relied upon.

I put some shock in about a month ago to kill off algae that had grown over the winter, and was surprised that chlorine levels are still high.

The water is the same as last year, except about 35% drained out due to a pipe detatching and was refilled with rain water. I've not added any stabilised chlorine this year, but added dichlor throughout last year.

I use a custom built air lift pump to circulate and filter the pool - this works as in a home aquarium aeration system. I wonder if this aeration is what is upsetting the PH test on the test paper strips for some reason, but I don't understand why the tablets are not being affected by this.

As an aside, the pool is shown to have a very high TA level, higher than our tap water which is already very high as we're in a hard water area.
The CYA level is shown as non existent - which is confusing since the chlorine doesn't appear to be disappearing and yet it's unstabilised shock (HypCal).

The only chemicals that have been in the pool are branded PH+ and PH-, Stabilised DiChlor, Algaecide (both copper based and non copper based), and Clarifier. All of these will now be much diluted with the 35% rain water top up the pool had over the winter.

The pool has a bubble cover on, and the water is crystal clear.

Many thanks for all and any thoughts or suggestions.

[Denniswiseman]

Aeration raises pH
Rain water is generally softer but acidic
Don't use copper algaecide as the effects aren't always desirable. Use a Polyquat 60
(Any brand as long as the ingredients are "Poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride" at 60% concentration.)

Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach) Liquid chlorine only adds salt
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA

Excessive CYA renders your chlorine ineffective and you have to use more to get the same sanitation
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm
To reduce your CYA you have to do a partial drain and refill
Continuous use of Trichlor/Dichlor will raise your CYA which means you have to raise your chlorine level as well

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Thank you for your thoughts on the products. That makes a lot of sense and its something I intend to do going forward. I did put a polyquat style algecide in it last year, but I had an issue with mustard algae and little tiny black spots like fly muck that took forever to get rid of, so added some old copper based algaecide too (it turned my son's white blonde hair a subtle green tinge the year before so had stopped). I figured in retrospect that the issue was the cya level had gotten too high for the chlorine to be effective. I track everything I use in a spreadsheet, so by my calculation based on the quantity of stabilised chlorine added, the cya level could have been as high as 186ppm. Now, even with the rain refill I suspect it is 98ppm, but the paper dip test shows it as zero which I find a little bizarre.... but then the PH test square isn't doing much sensible either.

[Teapot1]

Dip strip tests are notoriously bad, I swear the industry sell them to cause maximum confusion and therefore more trips to pool shops to spend on wonder products you dont need. Dip strips are particularly bad with CYA.

Shock is a process not a product, its simply raising the chlorine level to breakpoint where everything is killed and oxidised and it linked to the CYA level.
It is possible to loose all CYA over winter so go back to dichlor to raise it but only with a proper test, vanishing dot type will do.

If your TA is high I would expect your air lift pump to cause pretty quick pH rises. How much power does your airlift pump consume at what flow rate? I considered using an airlift pump a few years back but went a different route, how do you get on with backwashing the filter assuming you have a sand filter?

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Thanks. I agree with regard to the paper dip tests. I didn't know that they were especially bad for cya though. I went down that route because the alternative route of a tablet in a specially sized tube with a cross on the bottom was so expensive - I think it was about £70 with tablets more again. All the extra seem to cost a fortune for pools and what was I thought naiively a relatively cost effective form of garden entertainment has spiaraled wildly in both financial costs and time spent managing it since our original purchase of the pool kit.
The shock chlorine I have claims to have 17% more active chlorine than other chlorine shock products, but, I'm aware that the marketing forces as strong in the domain of pools. I try and get the full chemical names of products before assessing value for money, but this isn't simple online for shops I've found in the UK.

I thought that a TA meant that instigating a PH alteration cost more acid or base to effect a change - I've seen it referred to as a "buffer".

I think the thing about the air lift pump is that there is only so much oxygen and or co2 that the pool water can hold before it reaches saturation, so I find the PH is very stable. Typically the PH does not alter at all once the pump has been on for a few days, and I use it daily for an identical time throughout the UK brighter months (depending on year, it might be April - Novemeber) where I might consider using the pool, however short the session.

I don't use a sand filter, so I don't ever backwash it in the way I've read you do with those. I take the media out and wash it in the bath using a few litres of water, or washing machine roughly every week, then replace it. Really I should rinse it in a bucket and then use the water on the flowers, but I like to see the quantity of dust in the water for anecdotal confirmation of what is going on in the pool.

What I really need to find is somewhere that sells laundry bleach in the UK, ideally highstreet for convenience but could be online. I've seen you can get CYA in an expensive pot from some pool stores, so with these two products it would make things easier. Last time I looked, unscented household bleach was the best I found but the quantity of chlorine in it was a very low percentage.

The Polyquat algaecide is something I need to hunt for too - I have just finished the last on mine, but note it says 17% on it, so nothing like the 60% that the previous poster mentioned. Part of me thinks that maybe these strength chemicals just arent sold in quantities that a micro pool owner like myself would be able to use in a reasonable time frame.

[Teapot1]

Algaecide is a con, whilst many continue to misunderstand this. Chlorine is the best algaecide, polyquat is not measured in the pool so how much is enough, perfect for a pool shop, notice they dont sell test kits for it? Chlorine tries to oxidise, burn out anything it can so it will oxidise the polyquat meaning you add more chlorine as it gets used up quicker burning out the polyquat. So you buy more of both. If you use the correct level of chlorine in ratio to the CYA level you simply won't need polyquat.
I can look into the vanishing dot CYA tester for you next week when I am back in the UK but should be half what you have been quoted.
Yes for a given TA there is a given Co2 even at the low TA I use (40-50ppm) there is still 7 times more dissolved Co2 in the water than the air so the pH doesn't rise even after aeration. At a level of 120ppm the pH rises much more easily so again the pool industry benefits by selling more pH minus. TA does buffer pH but around pH 8.2, this is often offset by the CYA, being an acid it buffers also down around pH 6 so the combination gives a reasonably stable mid range pH.
Sounds like you are using pond media in your filter?

[Denniswiseman]

Liquid chlorine (sodium hypochlorite 14-15%) is readily available from pool stores
I've just purchased 4 x 20 litres for £30.00 each (The price has gone up dramaticly since Covid)

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Your understanding of the chemistry involved certainly reads like it exceeds my own.

Our tap water is, from reading the thames water water quality report, circa 280ppm (high calcium content). Initially I was really stressed about this because the pool kit said it should be below 150ppm if i recall correctly, but actually, it doesn't seem to cause a problem now I've stopped worrying about it. I gave up trying to push it low because it just made the pool too acidic and I was just burning through PH minus before eventually stressing and bringing it back to neutral with PH plus.

r.e. my filter, nothing so advanced - I investigated but I decided I didn't need anything better than what I'm using - just bits and pieces from around the home - in this case polyester teddy stuffing in a net. It's not as thorough a filter as denim, but once the pool is clear it is adequate to keep it that way.

What filtration and pump arrangement did you opt for instead of an air pump?

[Teapot1]

Our tap water is, from reading the thames water water quality report, circa 280ppm (high calcium content). Initially I was really stressed about this because the pool kit said it should be below 150ppm
What filtration and pump arrangement did you opt for instead of an air pump?

Are you talking calcium hardness or total alkalinity with that reading? TA is mainly all the carbonates disolved in the water.

I have a very good variable speed pump, slower filtration being better filtration (no breakthough of the media by dirt etc) set up to give 4 turnovers per day (98% of the water being filtered according to Gage and Bidwells theory of dilution) that is filtered through Dryden Aqua's AFM glass media. That's the original version not the newer AFM ng which I will fit at some point. Filtering to 1 micron, original version 5 microns.
The electricity consumption was one of my main aims so I use around 65 watts on filtration, somewhat better than the original 745 watts and with far higher water quality. The more you remove from the water the less there is for chlorine to do so consumption of chlorine also drops.

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From the report:
Alkalinity as CaCO: 278 mg/l
Hardness (Total) as CaCO3: 338 mg/l

From this when I quoted earlier I read the first figure as was in a rush, but I think that TA would actually be 338mg/l.

Your overall pump power consumption is impressive, I well remember the 500+W ratings from when I was looking into centrifugal pumps. I eventually was swayed by the air pump because I feel safer with it as I don't need to worry about switching it off while I'm in the pool. If the pool was built in and grounded and bonded then the centrifugal pump would be an option but otherwise, it just seemed counter intuitive to switch the pump off while using the pool in what was the hottest part of the day when chlorine wanted to be circulated best to avoid any issues. There is after all a reason that the commercial pool filtration works the entire time people are in the pool.
I don't know precisely what power my pump uses as I dont have a clamp meter to test it, but it is rated at 32watts. When the pool was green with algae a month ago, I ran it 12hrs a day for a week because I stupidly shocked before vaccuuming, but its now at 8hrs a day which I think will be more than enough throughout the year if I keep CYA levels in check (not like previous years when I had less understanding of the impact on the chlorine on high CYA levels).

Thank you for referencing the "Gage and Bidwells theory of dilution". I will read that. I think that I've read that once before, near the start of my journey there was too much to learn and it got dropped. It's actually why I opted to split my pumping into two distinct components - I wanted to maximise currents in the water while minimising speed of water travelling through the filter media, but I've not done the sums to prove the precise number of hours the pump must run to filter the entire pool. Luckily, with my pool being round, I can use stock tank circulation models of circulation and mixing of which more studies exist. It's difficult to do anything other than finger in the air without knowing the power of my circulation pump - I just know it is at least as powerful as the filter pump at the moment... but I've just now thought of a way to measure that so I'll check that and get back to you.

I'm not sure the micron size of my filter media, but cotton denim from an old pair of jeans (which I use and will until the water warms) has a good filtration quality according to this study quoted here https://www.huffingtonpost.co.uk/entry/best-coronavirus-face-mask-materials-new-study_l_5e99b576c5b6a92100e63129 allegedly catching 92% of 1 micron dust and 29% of 0.3 micron dust. The polyester fluff I've assumed to be 30% of 1 micron dust. I don't know these figures are accurate but what I know for a fact is that the paper cartridges, which don't quote a micron size, but one site I found claimed 20 micron, leave a lot of very fine dust in the pool that settles out and then when you get in, the pool goes hazy. Mine stays crystal clear when you get in and stir it up.

This is all really interesting to me, but has drifted way off the original topic of why the tablet test asserts my pool water and tap water have identical ph, while the paper dip test asserts (repeatably) that the tap water is as for the tablet test, while the pool water is very acidic. I emailed the manufacturer of the dip tests as I figured they'd be best equipped to answer this, but they have yet to return the email.

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Liquid chlorine (sodium hypochlorite 14-15%) is readily available from pool stores
I've just purchased 4 x 20 litres for £30.00 each (The price has gone up dramaticly since Covid)

Thanks, I'm not sure how I've missed this.

I've used these two websites amongst others for purchasing chemicals in the past (not a plug, no link to me at all), and none have sodium hypochlorite that I can see. https://www.ukpoolstore.co.uk, https://poolstore.co.uk/

I was considering going to a physical farm supplies shop for it, but I don't know enough about the product to know it will be the same chemical compound, though I presume it would be.

[Teapot1]

If you ask for the MSDS for the product it will tell you exactly what is in it. With the transport of dangerous goods it the transport costs rather than the bleach itself that puts the price up. Its the main driving force towards a salt chlorinator, add salt add a bit more power and you have on-site chlorine.

[Teapot1]

From the report:
Alkalinity as CaCO: 278 mg/l

I eventually was swayed by the air pump because I feel safer with it as I don't need to worry about switching it off while I'm in the pool. If the pool was built in and grounded and bonded then the centrifugal pump would be an option but otherwise, it just seemed counter intuitive to switch the pump off while using the pool in what was the hottest part of the day when chlorine wanted to be circulated best to avoid any issues.
I don't know precisely what power my pump uses as I dont have a clamp meter to test it, but it is rated at 32watts.

I wanted to maximise currents in the water while minimising speed of water travelling through the filter media, but I've not done the sums to prove the precise number of hours the pump must run to filter the entire pool. Luckily, with my pool being round, I can use stock tank circulation models of circulation and mixing of which more studies exist. It's difficult to do anything other than finger in the air without knowing the power of my circulation pump - I just know it is at least as powerful as the filter pump at the moment... but I've just now thought of a way to measure that so I'll check that and get back to you.

I'm not sure the micron size of my filter media, but cotton denim from an old pair of jeans (which I use and will until the water warms) has a good filtration quality according to this study quoted here https://www.huffingtonpost.co.uk/entry/best-coronavirus-face-mask-materials-new-study_l_5e99b576c5b6a92100e63129 allegedly catching 92% of 1 micron dust and 29% of 0.3 micron dust. The polyester fluff I've assumed to be 30% of 1 micron dust. I don't know these figures are accurate but what I know for a fact is that the paper cartridges, which don't quote a micron size, but one site I found claimed 20 micron, leave a lot of very fine dust in the pool that settles out and then when you get in, the pool goes hazy. Mine stays crystal clear when you get in and stir it up.

This is all really interesting to me, but has drifted way off the original topic of why the tablet test asserts my pool water and tap water have identical ph, while the paper dip test asserts (repeatably) that the tap water is as for the tablet test, while the pool water is very acidic. I emailed the manufacturer of the dip tests as I figured they'd be best equipped to answer this, but they have yet to return the email.

Good luck with getting any answer to your dip strip enquiries. Companies used to give theirs in some hope I might actually promote them, sadly even the ones from the likes of Palintet and Lovibond were still hopeless IMO. Most are jut white labelled from China and apart from the obvious printer's ink on the side of the packet never actually matching anything produced by the strip itself there are chemicals in a lot of pools that interfere with the reagents, one reason why I only add chlorine to my pool and apart from a little phosphate remover and ACO nothing else to interfere with the test results there is the dilution issue, 3 seconds or 5 in the pool water, wiggle or stationary, shake off the strip or not, tiny amount of reagent and other reagent chemicals running into one another on the strip all add up to junk test.

I dont switch off the pump when in the pool it is RCD protected but unless there is a pacemaker wearer (a reason not to have a salt chlorinator running) countless setups for expensive humans and Koi without an incident being reported AFAIK. That asside, I still considered the air pump early on for efficiency reasons as I did with looking into siphonic action with a tiny pump to prime the system. In my case just a separate pump for the backwash although to save water still using a bit of air scouring to assist.

Years back I paid a young graduate who was a whizz with computational fluidic software to map out the most efficient flow patterns for mixing of water for the filtration. That is why when I see a pool with skimmers at one end and returns at the other I know the pool builders have just copied the same errors they have made or copied other pool builders rather than learn what works best. Certainly round pools are better hydrodynamically speaking.

Thank you for the link to cotton/denim I shall take a look. There is a Turkish company producing a 1 micron easy backwashable filter which I was very tempted to purchase, it physically would remove the particles but in the case of AFM the surface activation also removes other contaminents but nevertheless interest to hear about your setup, the polyester fibre is known as a remover of iron from water supplies and may remove other contaminants, my only concern is micro plastics in the environment. Whereabouts are you in the UK, I would love to see your setup and I could bring my flow meter along to take some flow readings If you would allow?

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Electrical safety:

RCDs.... yes. you might like to do some research about those and how they are rated etc. I've come to the conclusion that they're not a safe form of protection if you're submerged in water that they're protecting. There is a reason that the pumps (mine at least) say "not to be used when people are in the pool". In modern British houses, consumer units also can have RCDs built in, so theoretically, you double your chances of one tripping quickly enough to stop a shock which makes things better, but if they were safe, pump suppliers would be happy to not place a bold capitalised warning on their products and the UK electrical regulations wouldn't mandate special bonding and grounding for pools where pumps are installed in a permanent fashion (i.e. not relevant for temporary splasher pools).

Because I've had two pumps which failed developing electrical faults, my confidence in the product itself isn't there, hence my move to the solution where the electricity is isolated from the pool by a length of air filled pipe. This gives me a much improved sense of wellbeing when guests are in the pool. If I were to install a heat pump, I'd no longer have this complete isolation from electricity I guess, but I don't think my pump would provide the necessary flow rate to use one in any case - they need substantially more litres per hour than my pump provides (well over double) to operate efficiently. I'd be concerned about the increased pressure drop stopping the pump working entirely too.

Microplastics:

Yes, point taken - I expect polyester fluff is highly unlikely not to shed microfibres. My whole filtration system has been built on a budget - initially because I could not justify a sand filter and appropriate pump setup, then the ongoing cost of electric to run it when the whole pool kit initially cost about £450. I'd be surprised if I've not spent close to the cost of a sand filter setup on my DIY solution as I've been experimenting, but I'd hope I've learned something along the journey. There's limits to how well I can make it work within the bounds of my toolkit.

Test Strips:

I take the point regarding the test strips and China - I've still not heard anything back from either seller nor manufacturer.... it doesn't bode well.

Gage and Bidwells theory of dilution:

I read a report on this and it reminded me why I lost interest - the theory appears to be on the basis that as water is filtered and returned to the pool, the cleaner water returned is immediately mixed 100% with the dirty water. This will only ever happen with a perfect system of circulation - in a splasher pool with a low power pump, the water comes back into the pool so slowly that there is really not much circulation going on at all - much less that 100% instantaneous. Not only that but inlet and outlet are in the same quadrant - I'd be amazed if with our original pump more than 1/4 of the pool water was being filtered each day (just many times over). It sounds like you've a substantially more powerful pump that will induce a flow in the pool and thus improve circulation substantially. In my case I've essentially added a circulation pump to my pool in conjunction with the filtration pump, but I'd still not go so far as to say there was immediately 100% dilution of the clean water returned.

ACO as a stabiliser:

I've read about the ACO you mention - that's really interesting. An alternative to CYA in a way, though it read to me like you'd burn chlorine quicker than if you maintained a static cya level of 15%+. I've started looking into sodium hypochlorite and I didn't fully appreciate how quickly it degrades - this makes it less cost effective for micro sized pools like mine as it has degraded further before each 10litre barrel is finished. I'm very tempted to try using both DiChlor and Sodium Hypochlorite this year though, using the DiChlor mainly to keep CYA levels useful. 1-200ml per week of ACO doesn't sound awful to avoid CYA for me, but what's missing from their marketing is chlorine consumption vs under a CYA regime.

AFM as a polyester fluff replacement:

The AFM filter media you mentioned looked interesting due to its self sterilising properties stopping things growing on it, maybe that would work instead of my polyester fluff if the back pressure were low enough.

On the whole, for the splasher pool I've got, the system that you use looks to be commercially unattractive, but it does look like something that might be of interest to someone with a pool more permanent in nature.

Location:

I'm in Berkshire, however I'd be embarrassed to show my setup at present. It is far from in an optimum configuration, and I suspect it would as a result be a disappointment. Flow meters can be used to measure the flow through the filter, I timed filling a bucket at a variety of air flow rates for this purpose. The circulation pump wouldn't be testable in this way though as there is by design no head. I'll see how long it takes to fill a carrier bag or similar when the weather improves.

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Fao Teapot1; For completeness and accuracy, I retested the flow today and the circulation pump is shifting 4100Lph, and the filter pump is shifting 1600Lph of water. I know these numbers could be improved, but the original pump supplied with the pool was rated at 2000Lph and actual system throughput was more like 1400Lph. Admittedly that pump was rated at 29watts not 32watts, but it also didn't last very long.